[Karl Ernst von Baer]

(in old age), from the picture by Hagen-Schwarz.

(By permission of the Berlin Photographic Company, 133 New Bond Street, London, W.)

HISTORY OF
BIOLOGY

BY

L. C. MIALL, D.Sc., F.R.S.,

FORMERLY PROFESSOR OF BIOLOGY IN THE UNIVERSITY OF LEEDS

[ISSUED FOR THE RATIONALIST PRESS ASSOCIATION, LIMITED]

London:

WATTS & CO.,

17 JOHNSON'S COURT, FLEET STREET, E.C.

1911

CONTENTS

PAGE

LIST OF ILLUSTRATIONS

PAGE

INTRODUCTION

Four hundred years ago, say in the year 1500, Biology, the science of life, was represented chiefly by a slight and inaccurate natural history of plants and animals. Botany attracted more students than any other branch, because it was recognised as a necessary aid to medical practice. The zoology of the time, extracted from ancient books, was most valued as a source from which preachers and moralists might draw impressive emblems. Anatomy and physiology were taught out of Galen to the more learned of physicians and surgeons. Some meagre notices of the plants and animals of foreign countries, mingled with many childish fables, eked out the scanty treatises of European natural history. It was not yet generally admitted that fossil bones, teeth, and shells were the remains of extinct animals.

It is the purpose of the following chapters to show how this insignificant body of information expanded into the biology of the twentieth century; how it became enriched by a multitude of new facts, strengthened by new methods and animated by new ideas.

The Biology of the Ancients.

Long before the year 1500 there had been a short-lived science of biology, and it is necessary to explain how it arose and how it became quenched. Ancient books and the languages in which they are written teach us that in very remote times men attended to the uses of plants and the habits of animals, gave names to familiar species, and recognised that while human life has much in common with the life of animals, it has something in common with the life of plants. Abundant traces of an interest in living things are to be found in the oldest records of India, Palestine, and Egypt. Still more interesting, at least to the inhabitants of Western Europe, is the biology of the ancient Greeks. The Greeks were an open-air people, dwelling in a singularly varied country nowhere far removed from the mountains or the sea. Intellectually they were distinguished by curiosity, imagination, and a strong taste for reasoning. Hence it is not to be wondered at that natural knowledge should have been widely diffused among them, nor that some of them should have excelled in science. Besides all the rest, the Greeks were a literary people, who have left behind them a copious record of their thoughts and experience. Greek science, and Greek biology in particular, are therefore of peculiar interest and value.

Greek naturalists in or before the age of Alexander the Great had collected and methodised the lore of the farmer, gardener, hunter, fisherman, herb-gatherer, and physician; the extant writings of Aristotle and Theophrastus give us some notion of what had been discovered down to that time.

Aristotle shows a wide knowledge of animals. He dwells upon peculiar instincts, such as the migration of birds, the nest-building of the fish Phycis, the capture of prey by the fish Lophius, the protective discharge of ink by Sepia, and the economy of the hive-bee. He is fond of combining many particular facts into general statements like these: No animal which has wings is without legs; animals with paired horns have cloven feet and a complex, ruminating stomach, and lack the upper incisor teeth; hollow horns, supported by bony horn-cores, are not shed, but solid horns are shed every year; birds which are armed with spurs are never armed with lacerating claws; insects which bear a sting in the head are always two-winged, but insects which bear their sting behind are four-winged. He traces analogies between things which are superficially unlike, such as plants and animals—the mouth of the animal and the root of the plant. The systematic naturalist is prone to attend chiefly to the differences between species; Aristotle is equally interested in their resemblances. The systematic naturalist arranges his descriptions under species, Aristotle under organs or functions; he is the first of the comparative anatomists. His conception of biology (the word but not the thing is modern) embraces both animals and plants, anatomy, physiology, and system. That he possessed a zoological system whose primary divisions were nearly as good as those of Linnæus is clear from the names and distinctions which he employs; but no formal system is set forth in his extant writings. His treatise on plants has unfortunately been lost.

Aristotle, like all the Greeks, was unpractised in experiment. It had not yet been discovered that an experiment may quickly and certainly decide questions which might be argued at great length without result, nor that an experiment devised to answer one question may suggest others possibly more important than the first. Deliberate scientific experiments are so rare among the Greeks that we can hardly point to more than two—those on refraction of light, commonly attributed to Ptolemy, and those by which Pythagoras is supposed to have ascertained the numerical relations of the musical scale. Aristotle was the last great man of science who lived and taught in Greece. His writings disappeared from view for many centuries, and when they were recovered they were not so much examined and corrected as idolised.

Greece lost her liberty at Chaeronea, and with liberty her fairest hopes of continued intellectual development. Nevertheless, during a great part of a thousand years the Greek and Semitic school of Alexandria cultivated the sciences with diligence and success. We must say nothing here about the geometry, astronomy, optics, or geography there taught, but merely note that Herophilus and Erasistratus, unimpeded by that repugnance to mutilation of the human body which had been insurmountable at Athens, made notable advances in anatomy and physiology. From this time a fair knowledge of the bodily structure of man, decidedly superior to that which Aristotle had possessed, was at the command of every educated biologist.

The genius of Rome applied itself to purposes remote from science. The example of Alexandria had its influence, however, upon some inhabitants of the Roman Empire. Galen of Pergamum in Asia Minor prosecuted the study of human anatomy. His knowledge of the parts which can be investigated by simple dissection was extensive, but he was unpractised in experimental physiology. Hence his teaching, though full with respect to the skeleton, the chief viscera, and the parts of the brain, was faulty with respect to the flow of the blood through the heart and body. Ages after his death the immense reputation of Galen, like that of Aristotle, was used with great effect to discredit more searching inquiries. Under the Roman Empire also flourished Dioscorides, who wrote on the plants used in medicine, and the elder Pliny, who compiled a vast, but wholly uncritical, encyclopædia of natural history.

We see from these facts how ancient nations, inhabiting the Mediterranean basin and largely guided by Greek intelligence, had not only striven to systematise that knowledge of plants and animals which every energetic and observant race is sure to possess, but had with still more determination laboured to create a science of human anatomy which should be serviceable to the art of medicine. The effort was renewed time after time during five or six centuries, but was at last crushed under the conquests of a long succession of foreign powers—Macedonians, Romans, Mohammedan Arabs, and northern barbarians—each more hostile to knowledge than its predecessors.

Extinction of Scientific Inquiry.

The decline and fall of the Roman Empire brought with it the temporary extinction of civilisation in a great part of Western Europe. Science was during some centuries taught, if taught at all, out of little manuals compiled from ancient authors. Geometry and astronomy were supplanted by astrology and magic; medicine was rarely practised except by Jews and the inmates of religious houses. Literature and the fine arts died out almost everywhere.

No doubt the practical knowledge of the farmer and gardener, as well as the lore of the country-side, was handed down from father to son during all the ages of darkness, but the natural knowledge transmitted by books suffered almost complete decay. The teaching ascribed to Physiologus is a sufficient proof of this statement. Physiologus is the name given in many languages during a thousand years to the reputed author of popular treatises of zoology, which are also called Bestiaries, or books of beasts. Here it was told how the lion sleeps with open eyes, how the crocodile weeps when it has eaten a man, how the elephant has but one joint in its leg and cannot lie down, how the pelican brings her young back to life by sprinkling them with her own blood. The emblems of the Bestiaries supplied ornaments to mediæval sermons; as late as Shakespeare's day poetry drew from them no small part of her imagery; they were carved on the benches, stalls, porches, and gargoyles of the churches.

In the last years of the tenth century A.D. faint signs of revival appeared, which became distinct in another hundred years. From that day to our own the progress has been continuous.

Revival of Knowledge.

By the thirteenth century the rate of progress had become rapid. To this age are ascribed the introduction of the mariner's compass, gunpowder, reading glasses, the Arabic numerals, and decimal arithmetic. In the fourteenth century trade with the East revived; Central Asia and even the Far East were visited by Europeans; universities were multiplied; the revival of learning, painting, and sculpture was accomplished in Italy. Engraving on wood or copper and printing from moveable types date from the fifteenth century. The last decade of this century is often regarded as the close of the Middle Ages; it really marks, not the beginning, but only an extraordinary acceleration, of the new progressive movement, which set in long before. To the years between 1490 and 1550 belong the great geographical discoveries of the Spaniards in the West and of the Portuguese in the East, as well as the Reformation and the revival of science.

PERIOD I.

1530-1660

Characteristics of the Period.

This is the time of the revival of science; the revival of learning had set in about two centuries earlier. Europe was now repeatedly devastated by religious wars (the revolt of the Netherlands, the wars of the League in France, the Thirty Years' war, the civil war in England). Learning was still mainly classical and scholastic; nearly every writer whom we shall have occasion to name had been educated at a university, and was able to read and write Latin. Two great extensions of knowledge helped to widen the thoughts of men. It became known for the first time that our planet is an insignificant member of a great solar system, and that Christendom is both in extent and population but a small fraction of the habitable globe.

The Revival of Botany.

Botany was among the first of the sciences to revive. Its comparatively early start was due to close association with the lucrative profession of medicine. Medicine itself was slow to shake off the unscientific tradition of the Middle Ages, and its backwardness favoured, as it happened, the progress of botany. In the sixteenth century the physician was above all things the prescriber of drugs, and since nine-tenths of the drugs were got from plants, botanical knowledge was reckoned as one of his chief qualifications. All physicians professed to be botanists, and every botanist was thought fit to practise medicine.

[From Fuchs' "Historia Stirpium",] 1542. The original occupies a folio page.

Figure of Solomon's Seal.

Three Germans, who were at once botanists and physicians—Brunfels, Bock, and Fuchs—led the way by publishing herbals, in which the plants of Germany were described and figured from nature. Their first editions appeared in the years 1530, 1539, and 1542. Illustrated herbals were then no novelty, but whereas they had hitherto supplied figures which had been copied time after time until they had often ceased to be recognisable, Brunfels set a pattern of better things by producing what he called "herbarum vivæ eicones," life-like figures of the plants. Each of the three new herbals contained hundreds of large woodcuts. Those engraved for Fuchs are probably of higher artistic quality than any that have appeared since. Each plant, drawn in clear outline without shading, fills a folio page, upon which the text is not allowed to encroach. The botanist will, however, remark that enlarged figures are hardly ever given, so that minute flowers show as mere dots, and that the details of the foliage are not so scrupulously delineated as in modern figures. The text of Brunfels and Fuchs is of little interest, being largely occupied with traditional pharmacy. Bock, whose figures are inferior to those of Brunfels and Fuchs, makes up for this deficiency by his graphic and sometimes amusing descriptions. He delights in natural contrivances, such as the hooks on the twining stem of the hop, or the elastic membrane which throws out the seeds of wood-sorrel. Brunfels has no intelligible sequence of species; Fuchs abandons the attempt to discover a natural succession, and adopts the alphabetical order; Bock aims at bringing together plants which show mutual affinity ("Gewächs einander verwandt"), though such natural groups as he recognises are neither named nor defined.

[Leonhard Fuchs.]
From his Historia Stirpium, 1742.

These three German herbals really deserve to be called scientific. To figure the plants of Germany from the life, to exclude such as existed only in books, and to strive after a natural grouping, was a first step towards a fruitful knowledge of plant-life. It is worth while to dwell for a moment upon the place where these herbals were produced. Along the Rhine civilisation and industry had for many years flourished together. Here and in the country to the east of the great river had sprung up that powerful union of seventy cities known in the thirteenth century as the Confederation of the Rhine; four universities, three of them on the banks of the Rhine, had been founded; here printing and wood-engraving had established themselves in their infancy; here, too, the Reformation found many early supporters. There were historical, economic, and moral reasons why the first printed books on natural history, illustrated by woodcuts drawn from the life, should have been produced in the Rhineland, and why all their authors should have been Protestants. Nearly every sixteenth-century botanist held the same faith.

The success of the first German herbalists brought a crowd of botanists into the field, among whom were several whose names are still remembered with honour. Gesner of Zurich made elaborate studies for a great history of plants, which he did not live to complete. It was he who first pointed out that the flower and fruit give the best indications of the natural relationships of plants, and his many beautiful enlarged drawings set an example which has done much for scientific botany. Botanists began to understand what natural grouping means, and to recognise that truly natural groups are not to be invented, but discovered. The almost accidental succession adopted by Brunfels, the alphabetical succession of Fuchs, the division according to uses (kitchen-herbs, coronary or garland-flowers, etc.), and the logical, but too formal, method of Cesalpini, in which, as in modern classification, much use was made of the divisions in the ovary—all these were left behind. L'Obel separated, unconsciously and imperfectly, the Monocotyledons from the Dicotyledons, recognised several easily distinguished families of flowering plants (grasses, umbellifers, labiates, etc.), and framed the first synoptic tables of genera.

The Revival of Zoology.

While the physicians of the Rhineland were describing and figuring their native plants, the study of animals began to revive. Two very different methods of work were tried by the zoologists of the sixteenth century. One set of men, who may be called the Encyclopædic Naturalists, were convinced that books, and especially the books of the ancients, constituted the chief source of information concerning animals and most other things. They extracted whatever they could from Aristotle, Ælian, and Pliny, adding all that was to be learned from the narratives of recent travellers, or from the collectors of skins and shells. The books on which they chiefly depended, being for the most part written by men who had not grappled with practical natural history and its problems, were unfortunately altogether inadequate. Many of the statements brought together by the encyclopædic naturalists were ill-attested; some were even ridiculously improbable. If inferences from the facts were attempted—and this was rare—they were more often propositions of morality or natural theology than the pregnant thoughts which suggest new inquiries. Hence the encyclopædic plan, even when pursued by men of knowledge and capacity, such as Gesner and Aldrovandi, yielded no results proportional to the labour bestowed upon it; the true path of biological progress had been missed. Naturalists of another school described and figured the animals of their own country, or at least animals which they had closely studied. Rondelet described from personal observation the fishes of the Mediterranean; Belon described the fishes and birds that he had met with in France and the Levant. His Book of Birds (1555) is a folio volume in which some two hundred species are described and figured. The "naturel" (natural history of the species) contains many curious observations. Perhaps the best things in the book are two figures placed opposite one another and lettered in correspondence; one shows the skeleton of a bird, the other that of a man. The example of Rondelet and Belon was followed by other zoological monographers, who did more for zoology than all the learning of the encyclopædists.

Early Notions of System.

Simple-minded people, who do not feel the need of precision in matters of natural history, have in all ages divided animals into four-footed beasts which walk on the earth, birds which fly, fishes which swim, and perhaps reptiles which creep. This is the classification found in the Babylonian and Hebrew narratives of the great flood. Plants they naturally divide into trees and herbs. It was not very long, however, before close observers became discontented with so simple a grouping. They discovered that the bat is no bird, though it flies; that the whale is no fish, though it swims; that the snake comes nearer in all essentials to the four-footed lizard, and even to the beast of the field, than to the creeping earthworm. At a much later time they discovered that pod-bearing or rose-like herbs may resemble pod-bearing or rose-like trees more closely than all trees resemble each other. Moreover, a multitude of animals became known which cannot be classed as either beasts, birds, fishes, or reptiles, and a multitude of plants which cannot be classed as either trees or herbs.

Bird's Skeleton.
For comparison with human skeleton (opposite), lettered to show the answerable bones. From Belon's Book of Birds, 1555.

Human Skeleton.
For comparison with bird's skeleton (opposite), lettered to show the answerable bones. From Belon's Book of Birds, 1555.

Aristotle found himself obliged to rectify the traditional classification of animals in order to remove gross anomalies. When learning decayed the traditional classification came back. Thus the Ortus Sanitatis (first published in 1475, and often reprinted) adopts the division into (1) animals and things which creep on the earth; (2) birds and things which fly; (3) fishes and things which swim. No consistent primary division of plants was proposed by Greek or Roman, nor by anyone else until the seventeenth century A.D.

This conflict of systems should have raised questions concerning the nature of classification and the relative value of characters. Some of the most striking resemblances found among animals and plants are only superficial; others, though far less obvious, are fundamental. Whence this difference? Why should scientific zoology make so little of the place of abode and the mode of locomotion; so much of the mode of reproduction and the nature of the skeleton? The answers were vague, and even the questions were rare and indistinct. But a metaphorical term came into use which was henceforth more and more definitely associated with fundamental, as distinguished from adaptive, likeness. Such likeness was called affinity,[1] though no attempt was made to explain in what sense the term was to be understood. As late as the year 1835 one of the first botanists in Europe (Elias Fries) could say no more about affinity between species than that it was quoddam supernaturale, a supernatural property.

A tolerable outline of a classification of animals was attained much earlier than a tolerable classification of plants. The characters available for the classification of plants are, to begin with, less obvious than those which the zoologist can employ. Moreover, the botanists were restricted to a narrower view of their subject. Zoologists, though they were expected to bestow the best part of their time upon vertebrates, were encouraged to study all animals more or less. Botanists, on the other hand, were practically obliged to concentrate their attention upon the classification of the flowering plants. The physician, herb-collector, and gardener cared nothing about any plants except such as bear flowers and fruit; but of these they expected full descriptions, and were clamorous for a system which would enable even a tyro to make out every species with certainty and ease. The task set before the botanist was comparable in respect of difficulty with the construction of a detailed and completely satisfactory classification of birds, which zoology has never yet been able to produce, while for the sake of this long-unattainable object almost everything else in botany was neglected.

The First English Naturalists.

During the greater part of three centuries (1300 to 1600), while the revival of learning and science was proceeding actively in Italy, France, Switzerland, and the Rhineland, England lagged behind. Humanist studies were indeed pursued with eminent success in the England of Sir Thomas More, but there was little else for national pride to dwell upon. The re-opening of ancient literature, the outpouring of printed books, the Reformation, the new mathematics and astronomy, the new botany and zoology, were mainly the work of foreigners. Before the seventeenth century no Englishman was recognised as the founder of a scientific school.

Passing over Edward Wotton (1492-1555), who recast the zoology of Aristotle with very little effect upon the progress of biology, we may head the list of English naturalists with the name of William Turner (d. 1568), who wrote on the plants and birds of Britain. Turner was a Reformed preacher, who had been the college friend of Ridley and Latimer. Being banished for preaching without licence, he studied medicine and botany in Italy, at Basle and at Cologne. Under Edward VI. he returned to England and was made Dean of Wells, fled again to the Continent on Mary's accession, was re-instated by Elizabeth, was suspended for non-conformity, and died not long after. Turner's herbal (1551-63) cannot be said to have done much for English botany. The arrangement is alphabetical, the properties and virtues of the plants are described out of ancient authors, and most of the figures are borrowed. Still, it was something to have the common plants of England examined by a man who had studied under Luke Ghini, had botanised along the Rhine, and was the pupil, friend, and correspondent of Conrad Gesner, the most learned naturalist in Europe. Turner's History of Birds (Historia Avium) was published in Latin at Cologne in 1544,[2] and is therefore earlier than Belon's book of birds. The history contains here and there among passages culled from the ancients a sprightly description of the feeding or nest-building of some English bird, and furnishes evidence of the breeding in our islands of birds which, like the crane, have long been known to us only as rare visitants. Of the kite Turner says that in the cities of England it used to snatch the meat out of the hands of children. In his day the osprey was better known to Englishmen than they liked, for it emptied their fishponds; anglers used to mix their bait with its fat. Turner shows not a little of that spirit of close observation which in a later and more tranquil age shone forth in Gilbert White.

Dr. John Caius (the name is supposed to be a Latinised form of Kay), the second founder of a great Cambridge college, was physician in succession to Edward VI., Mary, and Elizabeth; in his youth he had studied under Vesalius at Padua. Like Turner he was a friend and correspondent of Gesner, for whom he wrote an account of the dogs of Britain (De Canibus Britannicis, printed in Latin in 1570), which attempts to classify all the breeds, and to give some account of the uses to which each was put. The list contains no bull-dog, pointer, or modern retriever. There is a water-spaniel, however, and dogs had already been trained to retrieve game. The turnspit, which was not a distinct breed (Caius calls it a mongrel), has long been superseded. Curious antiquarian information, such as mention of the weapons formerly used by sportsmen, and obsolete names of dogs, reward the reader of this short tract.

Thomas Moufet wrote (for Gesner again) a book on insects, which incorporated the notes of Penny and Wotton. None of the three lived to see the printed book, which was at last put forth by Sir Thomas Mayerne in 1634. It is uncritical, confused, and illustrated by the rudest possible woodcuts.

John Gerarde's Herbal (1597) and Parkinson's two books of plants are more amusing than valuable. Both authors were guilty of unscrupulous plagiarism, a vice which cannot be atoned for by curious figures and bits of folk-lore, nor even by command of Shakespearean English. Thomas Johnson's edition of Gerarde (1633) is a far better book than the original; Ray called it "Gerarde emaculatus"—i.e., freed from its stains.

The succession of influential English naturalists may be said to begin with Ray, Willughby, and Martin Lister, all of whom belong to the last half of the seventeenth century.

The Rise of Experimental Physiology.

1543 is a memorable year in the history of science. Then appeared the treatise of Copernicus on the Revolutions of the Heavenly Bodies, completed long before, but kept back for fear of the cry of novelty and absurdity which, as he explains in his preface, dull men, ignorant of mathematics, were sure to raise. The aged astronomer, paralysed and dying, was able to hold his book in his hands before he passed away. In the same year Vesalius, a young Belgian anatomist, published his Structure of the Human Body, a volume rich in facts ascertained by dissection. Some of these facts were held to contradict the teaching of Galen. Next year Vesalius was driven by the hostility of the medical profession to burn his manuscripts and relinquish original work; he was not yet thirty years of age.

Galen had taught that there are two sets of vessels in the body (arteries and veins), and that in each set there is an ebb and flow. Knowing nothing of communications between the ultimate branches of the arteries and veins, and shrinking from the supposition that the arteries and veins are entirely separate and distinct, Galen had taught that the blood passes from one set of vessels to the other in the heart. The septum between the ventricles must be porous and allow the blood to soak through. Vesalius did not venture openly to challenge the physiology of Galen, but he significantly admired the "handiwork of the Almighty," which enables the blood to pass from the right to the left ventricle through a dense septum in which the eye can perceive no openings. Fabricius of Acquapendente in 1574 demonstrated the valves of the veins, though he never arrived at a true notion of their action. His celebrated pupil, William Harvey, who had been anticipated on important points by the Spaniard Michael Servetus and Realdo Columbo of Cremona, published in 1628 a clear account, supported by adequate experimental evidence, of the double circulation through the body and the lungs, and of the communications between the arteries and the veins in the tissues—communications which it was reserved for the next generation to demonstrate by the microscope.

Aselli of Cremona rediscovered the lacteals in 1622; they had been known ages before to Erasistratus, but forgotten. Opening the abdomen of a dog, he saw a multitude of fine white threads scattered over the mesentery, and observed that when one of them was pricked a liquid resembling milk gushed out. Further examination showed him that these vessels, like the veins, possess valves which permit flow in one direction only. Pecquet, a French physician, announced in 1651 that the lacteals open into a thoracic duct, which joins the venous system. In 1653 Rudbeck of Upsala described yet another set of vessels, the lymphatics; these again are provided with valves, and open into the thoracic duct, but are filled with a clear liquid.

The effect of these discoveries upon physiology and medicine was very great, but it did not end there; the whole circle of biological students and a still wider circle of men who pursued other sciences were thereby encouraged to follow the experimental path to knowledge. Wallis, in describing the meetings of scientific men held in London in 1645 and following years, mentions the circulation of the blood, the valves in the veins, the lacteals, and the lymphatic vessels among the subjects which had stirred their curiosity; while the naturalist Ray thanked God for permitting him to see the vain philosophy which had pervaded the University in his youth replaced by a new philosophy based upon experiment—a philosophy which had established the weight and spring of the air, invented the telescope and the microscope, and demonstrated the circulation of the blood, the lacteals, and the thoracic duct.

The Natural History of Distant Lands (Sixteenth Century and Earlier).

Travel and commerce had made the ancient world familiar with many products of distant countries. Well-established trade routes kept Europe in communication with Arabia, the Persian Gulf, and India. Egyptians, Phœnicians, and Greeks explored every known sea, and brought to Mediterranean ports a variety of foreign wares. Under the Roman empire strange animals were imported to amuse the populace; silk, pearls, gay plumage, dyes, and drugs to gratify the luxury of the rich.

Long after the fall of the empire foreign trade was kept up along the coasts of the Mediterranean. Constantinople was still a great emporium. Silk was not only imported from the East, but cultivated around Constantinople in the sixth century. The cotton plant, the sugarcane, the orange tree, and the lemon tree gradually spread northward and westward until they became established in Italy, Spain, and the islands of the Mediterranean.

Western Europe had during many centuries little share in this commerce. The large and conspicuous animals of Africa and Asia, such as the elephant, camel, camelopard, ostrich, pelican, parrot, and crocodile, would have passed out of knowledge altogether but for chance mention in the Bible and the Bestiaries. Little was done to supplement native food-plants and drugs by imported products, and the knowledge of foreign vegetation became as indistinct as that of foreign animals.

In the thirteenth century communication between Western Europe and the far East was restored. China was thrown open by the Tartar conquest, and Marco Polo was able to reach the court of Khan Kublai. Pilgrims from the Holy Land brought back information which, however scanty it might be, was eagerly received. One of the earliest printed books (1486) contains the travels of Bernard of Breydenbach, a canon of Mainz, whose narrative is adorned by curious woodcuts, in which we can make out a giraffe and a long-tailed macaque.

The geographical discoveries of the sixteenth century gave men for the first time a fairly complete notion of the planet which they inhabit. Circumnavigators proved that it is really a globe. Maps of the world, wonderfully exact considering the novelty of the information which they embodied, were engraved as early as 1507. The explorers of America busied themselves not only with the preparation of charts, the conquest of Mexico and Peru, the search for gold, and the spread of the true faith, but also with the strange animals and plants which they saw; and the news which they brought back was eagerly received in Europe. Queen Isabella charged Columbus, when he set out for his second voyage, to bring her a collection of bird-skins; but this may be rather a proof of her love of millinery than of her interest in natural history. Pope Leo X. liked to read to his sister and the cardinals the Decades of Peter Martyr Anglerius,[3] in which the productions of the New World are described. The opossum, sloth, and ant-eater, the humming-bird, macaw, and toucan, the boa, monitor, and iguana, were made known for the first time. Potatoes and maize began to be cultivated in the south of Europe, the tomato was a well-known garden plant, the prickly pear was spreading along the shores of the Mediterranean, and tobacco was largely imported. By the end of the seventeenth century Mirabilis and the garden Tropæolum had been brought from Peru, the so-called African marigold from Mexico, and sunflowers from North America. More than a hundred years had still to run before the evening primrose, the passion flower, and the lobelias of America were to become familiar to European gardeners, ipecacuanha and cinchona to European physicians.

Agriculture, Horticulture, and Silk-Culture in the Sixteenth Century.

During the darkest parts of the Middle Ages agriculture and horticulture were regularly practised. Tyranny, the greed of settlers, the inroads of barbarians, private war, and superstition may destroy all that brightens human life, but they hardly ever exterminate the population of large districts,[4] and so long as men live they must till the soil.

The age of Charlemagne was one of cruel hardship to the inhabitants of Western Europe, but the cartularies of the great king show that the improvement of horticulture was a matter of much concern with him. The nobles and the religious houses kept trim gardens, which are delineated in mediæval paintings. We know less about the state of the peasantry, but it is clear that they ploughed, sowed, reaped, and dug their little gardens, however uncertain the prospect of enjoying the produce of their labour.

The progressive Middle Ages (about 1000 to 1500 A.D.) greatly increased the comfort of the wealthy and alleviated the miseries of the poor. We now hear of countries (England, the Low Countries, the western half of Germany, the northern half of Italy) where freemen cultivated their own land, or grew rich by trade, and these men were not content barely to support life. Under the later Plantagenets the wool-growers of that upland country which stretches from Lincolnshire to the Bristol Channel showed their wealth by building a profusion of manor-houses and beautiful perpendicular churches, many of which still remain. There can be little doubt that they were attentive to the rural industries which are so great a source of comfort and pleasure.

In the sixteenth and seventeenth centuries the Flemings, a laborious and enterprising people, inhabiting a fertile country, excelled the rest of Europe in agriculture and horticulture. L'Obel, himself a Fleming, speaks with pride of the live plants imported into Flanders from Southern Europe, Asia, Africa, and America. By the close of the sixteenth century, or a few years later, the lilac, lavender, marigold, sun-flower, tulip, and crown-imperial, the cucumber and garden rhubarb, besides many improved varieties of native vegetables, were sent out from Flanders to all parts of Western Europe. During many generations English agriculture and horticulture, and not these alone, but English ship-building, navigation, engineering, and commerce as well, looked to the Low Countries as the chief schools of invention and the chief markets from which new products were to be obtained.

Late in the sixteenth century a gentleman of the Vivarais (the modern Ardèche), named Olivier de Serres, wrote a book on the management of land,[5] which leaves a strong impression of the zeal for improvement which then pervaded Europe. De Serres was above all things intent upon extending silk-culture in France. On this topic he wrote with full knowledge, having reared silkworms for thirty-five years. The King, Henri Quatre, shared his hopes, and gave him practical encouragement. It is well known that a great industry was thus started; by 1780 the annual yield of silk-cocoons in France was valued at near a million sterling, while in 1848 it had risen to four millions. De Serres sought to promote the cultivation of the mulberry tree, not only because its leaves are the food of the silkworm, but because he believed that the fibres of the bast would be serviceable in the manufacture of cordage and cloth. He also tried to revive the ancient practice of hatching eggs by artificial heat. We learn from him that the turkey, recently introduced from Mexico, had already become an important addition to the poultry-yard, while maize from Mexico and beetroot from the Mediterranean coasts were profitable crops. Among the new appliances De Serres mentions artificial meadows, wind and water-mills, cisterns not hewn from stone, and greenhouses.

[1] Aristotle, Cesalpini, Gesner, and Ray are among the writers who use this word or some synonym.

[2] It has now been made accessible to all readers by the reprint and translation of Mr. A. H. Evans.

[3] Letter of Peter Martyr, Dec. 26, 1515.

[4] The extermination of the red man in North America is the most conspicuous case recorded in history. Australia and Tasmania furnish examples on a smaller scale.

[5] Le Théâtre d'Agriculture, 1600.

PERIOD II

1661-1740

Characteristics of the Period.

In Western Europe this was a time of consolidation succeeding to one of violent change. Religious wars gave place to dynastic and political wars. In France the tumults of the preceding hundred years sank to rest under the rule of a strong monarchy; order and refinement became the paramount aims of the governing classes; literature, the fine arts, and the sciences were patronised by the Court. Other nations imitated as well as they could the example of France. Learning was still largely classical, but the anti-scholastic revolt, which had first made itself felt three hundred years earlier, steadily gained ground; Descartes, Newton, and Locke were now more influential than the Aristotelians. This was an age of new scientific societies (Royal Society, Academy of Sciences of Paris, Academia Naturæ Curiosorum, etc.).

The Minute Anatomists.

Magnifying glasses are of considerable antiquity. Seneca mentions the use of a glass globe filled with water in making small letters larger and clearer. Roger Bacon (1276) describes crystal lenses which might be used in reading by old men or those whose sight was impaired. As soon as Galileo had constructed his first telescopes, he perceived that a similar instrument might be caused to enlarge minute objects, and made a microscope which revealed the structure of an insect's eye. Within twenty years of this date the working opticians of Holland, Paris, and London sold compound microscopes, which, though cumbrous as well as optically defective, revealed many natural wonders to the curious. Simple lenses, sometimes of high power, came before long to be preferred by working naturalists, and it was with them that all the best work of the seventeenth and eighteenth centuries was done.

The power of the microscope as an instrument of biological research was in some measure revealed by Hooke's Micrographia (1665). Robert Hooke was a man of extraordinary ingenuity and scientific fertility, who took a leading part in the early work of the Royal Society. He opens his book with an account of the simple and the compound microscope of his own day, and then goes on to explain, with the help of large and elaborate engraved plates, the structure of a number of minute objects. The most interesting are: A Foraminiferous shell, snow-crystals, a thin section of cork showing its component cells, moulds, a bit of Flustra, the under side of a nettle-leaf with its epidermic cells and stinging-hairs, the structure of a feather, the foot of a fly, the scales of a moth's wing, the eye of a fly, a gnat-larva, and a flea. The beauty of the plates and the acuteness of some of the explanations are remarkable, but lack of connection between the topics discussed hinders the Micrographia from rising to a very high scientific level.

Swammerdam treated the microscope as an instrument of continuous biological research. In his eyes it was a sacred duty to explore with the utmost faithfulness the minute works of the Creator. Insects yielded him an inexhaustible supply of natural contrivances, in which closer scrutiny always brought to view still more exquisite adaptations to the conditions of life. He was able to throw a beam of steady light upon the perplexed question of insect-transformation, and swept from his path the sophistries with which the philosophy of the schools had obscured the change of the caterpillar into a moth, or of the tadpole into a frog. He demonstrated the gradual progress of the apparently sudden transformation of certain insects by dipping into boiling water a full-fed caterpillar, and then exposing the parts of the moth or butterfly, which had almost attained their complete form beneath the larval skin; after this it was easy to discover the same parts in the pupa.

There is no more valuable chapter in Swammerdam's great work, the Biblia Naturæ, or Book of Nature, than that devoted to the hive-bee. This insect had long been a favourite study, but only those who were armed with a microscope and skilled in minute anatomy could solve the many difficult questions with which it was involved. Aristotle and other ancient naturalists had spoken of the king of the bees, which some bee-masters of the seventeenth century had been inclined to call the queen. Was it really true that the queen was a female, perhaps the only female in the hive? This question Swammerdam decided by the clearest anatomical proof—viz., by dissecting out her ovaries. He pointed out the resemblances between the queen and the workers, such as the possession of a sting by both, but did not discover the reduced reproductive organs of the workers, and wrongly declared that they never lay eggs. He proved by elaborate dissections that the drones are the males of the community. How and when the queen is fertilised he could not make out.

Marcello Malpighi.

From an engraving of the oil-painting by A. M. Tobar, presented to the Royal Society by Malpighi.

The dissection of the sting, the proboscis, and the compound eye of the bee was a task after Swammerdam's own heart, but so intricate that all his patience and skill could not save him from occasional slips. He bequeathed to his successors many noble examples of the way in which life-histories ought to be investigated.

Malpighi of Bologna may be called the first of the histologists, for as early as the second half of the seventeenth century he unravelled the tissues of many animals and plants. His work on plant-tissues was so closely accompanied by the similar researches of an Englishman, Nehemiah Grew, that it is not easy to assign the priority to either. Malpighi was the first to demonstrate the capillaries which connect the arteries with the veins, the first to investigate the glands of the human body and the sensory papillæ of the skin. At the request of our Royal Society he drew up an account of the structure and life-history of the silkworm, which is memorable as the earliest anatomical study of any insect. Malpighi also applied his microscope to the chick-embryo, and figured its chief stages. His exposition of the formation of the heart and vessels of the chick is a marvellous example of the quick appreciation of novel structures.

If we suppose the Micrographia of Hooke to be greatly enlarged, so as to become, instead of the passing occupation of a man busied with a hundred other interests, the main pursuit of a long and laborious life, we shall get a rough notion of the microscopic revelations of Leeuwenhoek. His researches were desultory, though not quite so desultory as Hooke's; he must have often spent months upon an investigation which Hooke would have dismissed in as many weeks. Both travelled over the whole realm of nature, and lacked that concentration which made the work of Swammerdam so productive and so lasting.

Antony van Leeuwenhoek.

From the portrait by Verkolje, prefixed to the Epistolæ ad Soc. Reg. Angl., Leyden, 1719.

Leeuwenhoek worked with simple lenses, ground and mounted by his own hands. It was easy to make lenses of high magnifying power, but hard to correct their optical defects, to bring a sufficiently strong light to bear upon the object, and to focus the lens. When he wished to send out his preparations for examination by others, he found it best to fix the objects in the focus, and to provide each with a separate lens. With such microscopes he managed to study and figure very minute objects, such as blood-corpuscles, spermatozoa, and bacteria. The spermatozoa were brought under his notice by a young Dutch physician named Hamm; but it was Leeuwenhoek's account of them, and his daring theory of their physiological rôle, which gave them such celebrity. To Leeuwenhoek we owe the first discovery of the rotifers, the infusoria, Hydra, the yeast-cell, the bacteria, and the generation of aphids without male parents.

The tradition of the minute anatomists has never been lost, though we shall be unable to pursue it in these pages. Lyonet (see p. 61) even surpassed Swammerdam in the elaborate finish of some of his insect-dissections.

Early Notions about the Nature of Fossils.

Throughout the sixteenth century naturalists held animated debates about the shells which are found far from the sea, and even on the top of high hills. Had they ever formed part of living animals or not? Such a question could hardly have been seriously discussed among simple-minded people; but the learned men of the sixteenth century were rarely simple-minded. They had been trained to argue, and argument could make it plausible that such shapes as these were generated by fermentation or by the influence of the stars. So prevalent were these doctrines that it entitles any early philosopher to the respect of later generations that he should have taken shells, bones, and teeth to be evidences of animal life. In this singular roll of honour we find the names of Cesalpini, Palissy, Scilla, Stenson, Hooke, and Woodward.

In England the struggle between philosophy and common-sense was long kept up. Dr. Ralph Cudworth of Cambridge taught that there is in nature a subordinate creative force of limited power and wisdom, to whose imperfections may be attributed the "errors and bungles" which now and then mar the work. To this subordinate creative force he gave the name of "vegetative soul," or "plastic nature." None but Cambridge men, it would appear, felt the weight of Cudworth's reasoning; but several of these, and especially John Ray[6] and Martin Lister, defended his conclusions in published treatises. Lister, in a chapter devoted to "cochlites," or shell-shaped stones, pointed out that they differ from true shells in being of larger size, in occurring far from the sea, in being formed of mere stony substance, and in being often imperfect. Some naturalists had conjectured that the living animals of the cochlites still exist at great depths in the sea, but Lister evidently thought otherwise.

In the eighteenth century the belief that fossils are the remains of actual animals and plants more and more prevailed, the death and sealing up of the organisms being generally attributed to Noah's flood. The occurrence of fossils on high mountains seemed so strong a confirmation of the Biblical narrative that Voltaire was driven to invent puerile explanations in order to dispel an inference so unwelcome to him. By the end of the century most naturalists accepted the doctrine that the great majority of fossils are the remains of organisms now extinct—a doctrine which was enforced by the remarkable discoveries of Cuvier (see p. 93). Nearly at the same time William Smith established the important truth that almost every fossil marks with considerable precision a particular stage in the earth's history.

Comparative Anatomy: the Study of Biological Types.

Between 1660 and 1740 the scope of natural history became sensibly enlarged. System had been hitherto predominant, but the systems had been partial, treating the vertebrate animals and the flowering plants with as much detail as the state of knowledge allowed, but almost ignoring the invertebrates and the cryptogams. System was now studied more eagerly than ever by such naturalists as Ray and Linnæus, but new aspects of natural history were considered, new methods practised, new groups of organisms included. Many remarkable vertebrates were anatomically examined for the first time. Claude Perrault and his colleagues of the Académie des Sciences dissected animals which had died in the royal menagerie, and compared the parts and organs of one animal with those of another; Duverney compared the paw of the lion with the human hand; in England Tyson studied the anatomy of the chimpanzee, porpoise, opossum, and rattlesnake, searching everywhere for the transitions which he believed to connect all organisms, and to form "Nature's Clew in this wonderful labyrinth of the Creation." The new microscopes helped to bring the lower and smaller animals into notice. From 1669, when Malpighi described the anatomy and life-history of the silkworm, a succession of what we now call biological types were studied; among these were many invertebrates. Edmund King and John Master contributed to Willis's treatise De Anima Brutorum (1672) the anatomies of the oyster, crayfish, and earthworm, all illustrated by clear and useful plates. Heide (1683) wrote an account of the structure of the edible mussel (Mytilus), in which mention is made of the ciliary motion in the gill; Poupart (1706) and Méry (1710) wrote accounts of the pond-mussel (Anodon). Swammerdam's elaborate studies of insects and their transformations were followed up by a long succession of memoirs by Frisch in Germany, Réaumur in France, and (shortly after the close of the period now under discussion) De Geer in Sweden. The extraordinary diligence and power of Swammerdam and Réaumur give a very prominent place in the biology of the seventeenth and eighteenth centuries to the structure and life-histories of insects. The great generalisations of comparative anatomy do not belong to this period; nevertheless, sagacious and luminous remarks are not wanting.

Adaptations of Plants and Animals: Natural Theology.

Natural adaptations and some of the problems which they suggest were much studied during this period. Bock and Cesalpini had discussed still earlier the mechanisms of climbing plants, aquatic plants, and plants which throw their seeds to a distance. Swammerdam figured, not for the first time, the sporangia and spores of a fern; Hooke the peristome of a moss. The early volumes of the Académie des Sciences contain many studies of natural contrivances. Perrault described the retractile claw of the lion, the pointed papillæ on its tongue, the ruminant stomach and the spiral valve of a shark's intestine. He improved upon Hooke's account of the structure of a feather, and his magnified figures of a bit of an ordinary quill and of a bit of an ostrich-plume might be inserted into any modern treatise on animal structure.[7] Poupart followed the later stages of the development of a feather. Méry gave a minute yet animated description of the wood-pecker's tongue, explaining how it is rendered effective for the picking up of insects, how it is protruded and retracted, how it is stowed away when not in use. Tournefort figured the oblique fibres of a leguminous pod, which he called muscles, and showed how they twist the valves and squeeze out the seeds.

Natural theology was much in the thoughts of the naturalists who studied and wrote between 1660 and 1740. Ray discoursed upon the Wisdom of God as manifested in the Creation. Swammerdam regularly closed the divisions of his Biblia Naturæ with expressions of pious admiration. A long list of books expressly devoted to the same theme might be given.[8] One weakness of the natural theologians was their habit of looking upon the universe as existing for the convenience of man. Still more fatal was the partiality with which they stated the facts. While they dwell upon the adaptations which secure the welfare of particular animals or plants, they are silent about the sufferings caused by natural processes.

Spontaneous Generation.

During many ages every naturalist thought that he had ample proof of the generation without parents of animals and plants. He knew that live worms appear in tightly-closed flasks of vinegar; that grubs may be found feeding in the cores of apples which show no external marks of injury; and that weeds spring up in gardens where nothing of the sort had been seen before. Certain kinds of animals and plants are peculiar to particular countries; what more likely than that they should be the offspring of the soil? Fables and impostures supported what all took to be facts of observation. The great name of Aristotle was used to confirm the belief that insects were bred from putrefaction; eels and the fishes called Aphyæ from the mud of rivers. A belief in a process of transmutation was often combined with a theory of spontaneous generation. Francis Bacon not only held that insects were born of putrefying matter, but that oak boughs stuck in the earth produced vines.

Towards the end of the seventeenth century it occurred to one inquiring mind that a particular case of spontaneous generation, which had been accepted by everybody without hesitation, was capable of a less mysterious explanation. Francesco Redi (1626-1698), physician to the Duke of Tuscany, published in 1668 an account of his experiments on the generation of blow-flies. He found that the flesh of the same animal might yield more than one kind of fly, while the same fly might be hatched from different kinds of flesh. He saw the flies laying their eggs in flesh, and dissected eggs out of their ovaries. When he kept off the flies by gauze the flesh produced no maggots, but eggs were laid on the gauze. Redi concluded that flies are generated from eggs laid by the females. He also studied insect-galls, and the worms which feed on growing seeds. Like earlier observers, he was baffled by finding live grubs in galls or nuts which were apparently intact, and by the parasitic worms which are now and then found in the brain-case and other closed cavities of quadrupeds. Such instances led him to jump at the supposition of a "vivifying principle," which generated living things of itself—a supposition contrary to the truer doctrine which he taught elsewhere. Vallisnieri was able to explain how the egg is introduced into the rose-gall, which a little later shows no mark of injury; while Malpighi examined the young nut and found both hole and egg. How parasitic worms reach the brain-case of the sheep could be explained only in a later age. Meanwhile Swammerdam, Leeuwenhoek, Réaumur, and many other special students confirmed and extended Redi's experiments on the blow-fly; and every fresh instance of normal generation in a minute organism did something to weaken the belief in spontaneous generation.

Late in the eighteenth century that belief revived in a form less easy of refutation. Leeuwenhoek had discovered that organic matter putrefying in water often yielded abundance of microscopic organisms of the most diverse kinds, many of which could resist drying in air and resume their activity when moistened again. Buffon, ever ready with a speculative explanation, maintained that such minute organisms were spontaneously generated, and that they were capable of coalescing into bodies of larger size and more complex structure. Needham supported Buffon's theories by experiments. Taking infusions of meat, corking them, and sealing them with mastic, he subjected them to a heat which he thought intense enough to destroy life; after an interval the microscope revealed an abundance of living things which he affirmed to have been generated from dead matter. Spallanzani repeated Needham's experiments with stricter precautions, sealed his flasks by fusing their necks in a flame, and then immersing them in boiling water until they were heated throughout. The infusions in such flasks remained limpid; no scum formed on the surface; no bad smell was given off when they were opened; and no signs of life could be detected by the microscope. To meet the objection that the vegetative force of the infusions had been destroyed by long heating he simply allowed air to enter, when the micro-organisms quickly reappeared. Spallanzani's methods, though far better than any which had been employed before, are not quite unimpeachable, and could not be relied upon in an atmosphere rich in germs; but they sufficed to create a strong presumption that life is set up in infusions by germs introduced with the air.

This was by no means the end of the controversy, which broke out again and again until it was laid to rest, whether finally or otherwise it would be unwise to predict, by the experiments of Pasteur.

The Natural History of John Ray.

The sixteenth, seventeenth, and eighteenth centuries each possessed at least one naturalist of wide learning and untiring diligence, who made it his care to collect information concerning all branches of natural history, to improve system, and to train new workers. Gesner, Ray, and Linnæus occupied in succession this honourable position.

Ray was originally a fellow of Trinity College, Cambridge, who had risen into notice by proficiency in academical studies. He then became inspired by the hope of enlarging the knowledge of plants and animals, and of producing what we should now call a descriptive fauna and flora of Great Britain. His plan contemplated close personal observation, travels at home and abroad, and the co-operation of pupils and friends.

[John Ray.]

From an old engraving of the portrait by Faithorn.

His chief assistant was Francis Willughby, a young man of wealth and good family; while Martin Lister, a Cambridge fellow, who had already laboured at natural history with good effect, undertook an independent share in the work. Ray wisely began with what lay close at hand, and published a catalogue of the plants growing around Cambridge. This was not a mere list of species, but a note-book charged with the results of much observation and reading. Journeys in quest of fresh material were begun. Then Ray's well-laid scheme was disconcerted by calamities which would have overwhelmed a less resolute man. He was driven from Cambridge by the Act of Uniformity, and forced to serve for years as a tutor in private families. When this servitude came to an end his only livelihood was a small pension, bequeathed to him by Willughby, on which he lived in rustic solitude. Willughby was cut off at the age of thirty-six, having accumulated much information but completed nothing. Lister became a fashionable physician, to whom natural history was little more than an elegant diversion. The whole burden of the enterprise fell upon Ray, who manfully bore it to the end. He completed his own share of the work, prepared for the press the imperfect manuscripts of Willughby, and before he died was able to fulfil the pledge which he had given forty years before in the prosperity of early manhood. It is needless to say that the natural history of Britain, executed in great part by a poor and isolated student, fell far short of what Ray might at one time have reasonably expected to accomplish.

Ray, like other early naturalists, saw that a methodical catalogue of species, arranged on some principle which could be accepted in all times and in all countries, was indispensable to the progress of natural history, and such a catalogue formed an essential part of his plan. Perhaps he was a little deficient in that discernment of hidden affinities which has been the gift of great systematisers, but his industry, learning, and candour accomplished much. Quadrupeds, birds, reptiles, fishes, insects, and plants of every sort were reviewed by him. British species naturally received special attention, but Ray did not fail to make himself acquainted with the natural productions of foreign countries, partly by his own travels, and partly by comparing the descriptions of explorers. He seized every opportunity of investigating the anatomy and physiology of remarkable animals and plants, and attended to the practical uses of natural history. British naturalists owed to him the first serviceable manuals for use in the field.

Ray was the first botanist who formally divided flowering plants into Monocotyledons and Dicotyledons. It was only natural that he should now and then have misplaced plants whose general appearance is deceptive (lily of the valley, Paris, Ruscus, etc.). He was perhaps the first to frame a definition of a species; but here his success, as might be expected, was not great. A species was with him a particular sort of plant or animal which exactly reproduces its peculiarities generation after generation. Any plant, for example, which comes up true from seed, would according to Ray constitute a species. By this definition many races of plants which are known to have been produced in nurseries would rank as true species.

The Scale of Nature.

No one can closely examine a large number of plants and animals without perceiving real or imaginary gradations among them. The gradation, shrews, monkeys, apes, man, is not very far from a real genealogical succession, confirmed by structural and historical proofs. The gradation, fish, whale, sheep, on the other hand, though it seemed equally plausible to early speculators, is not confirmed by structure and history. In the age of Aristotle and for long afterwards the ostrich was believed to be a connecting link between birds and mammals, because it possessed, in addition to obvious bird-like features, a superficial resemblance to a camel (long neck, speed in running, desert haunts, and a rather imaginary resemblance in the toes). Sedentary, branching zoophytes were quoted as intermediate between animals and plants; corals and barnacles as intermediate between animals or plants and stones. Aristotle was convinced of the continuity of nature; his scale of being extended from inanimate objects to man, and indicated, as he thought, the effort of nature to attain perfection. Malpighi traced analogies between plants and animals, identifying the seed and egg, as many had done before him, assuming that viviparous as well as oviparous animals proceed from eggs, and comparing the growth of metals and crystals with the growth of trees and fungi. Leibnitz believed that a chain of creatures, rising by insensible steps from the lowest to the highest, was a philosophical necessity. Buffon accepted the same conclusion, and affirmed that every possible link in the chain actually exists. Pope reasoned in verse about a "vast chain of being," which reaches from God to man, and from man to nothing. The eighteenth century was filled with the sound.

Bonnet in 1745 traced the scale of nature in fuller detail than had been attempted before. He made Hydra a link between plants and animals, the snails and slugs a link between mollusca and serpents, flying fishes a link between ordinary fishes and land vertebrates, the ostrich, bat, and flying fox links between birds and mammals. Man, endowed with reason, occupies the highest rank; then we descend to the half-reasoning elephant, to birds, fishes, and insects (supposed to be guided only by instinct), and so to the shell-fish, which shade through the zoophytes into plants. The plants again descend into figured stones (fossils) and crystals. Then come the metals and demi-metals, which are specialised forms of the elemental earth. Water, air, and fire, with perhaps the æther of Leibnitz, are placed at the bottom of the scale.

In Bonnet's hands the scale of nature became an absurdity, by being traced so far and in so much detail. It was not long before a reaction set in. The great German naturalist, Pallas, in his Elenchus Zoophytorum (1766) showed that no linear scale can represent the mutual relations of organised beings; the branching tree, he said, is the appropriate metaphor. Cuvier taught that the animal kingdom consists of four great divisions which are not derived one from another, and his authority overpowered that of Lamarck, who still maintained that all animals form a single graduated scale. A complete reversal of opinion ensued, so complete that at length the theologians, who had once seen in the scale of nature a proof of the wisdom of Providence, were found fighting with all their might against the insensible gradations which, according to Darwin's Origin of Species, must have formerly connected what are now perfectly distinct forms of life.

The eighteenth-century supporters of continuity in nature were not merely wrong in picturing the organised world as a simple chain or scale. They were also wrong in assuming that all the links or steps still exist. We can now see that vast numbers are irrecoverably gone. It is a safe prophecy that the filiation of species will never be grasped by the intelligence of man except in outline, and even an outline which shall truly express the genetic relations of many chief types is unattainable at present.

The Sexes of Flowering Plants.

As soon as men began to raise plants in gardens, or even earlier, they must have remarked that plants produce seeds, and that seeds develop into new plants. The Greeks (Empedocles, Aristotle, Theophrastus) recognised that the seed of the plant answers to the egg of the animal, which is substantially though not literally true. None of the three understood that a process of fertilisation always, or almost always, precedes the production of seed. Had the date-palm, whose sexes are separate, and which has been artificially fertilised from time immemorial, been capable of cultivation in Greece, Aristotle would not have said that plants have no sexes, and do not require to be fertilised. His pupil, Theophrastus, knew only by hearsay of the male and female date-palms, and affirmed that both bear fruit. Pliny, three hundred years later, called pollen the fertilising substance, and gave it as the opinion of the most competent observers that all plants are of two sexes. The revivers of botany paid no attention to pollen or the function of the flower; it is more surprising that in the following century Malpighi, who had diligently studied the development of the plant-embryo, should give so superficial an account of the stamen and its pollen. About the same time Grew and Millington expressed their conviction that "the attire" (anthers) "doth serve as the male, for the generation of the seed."[9] A few years later Ray[10] speaks of the masculine or prolific seed contained in the stamens. In 1691-4 Camerarius, professor at Tübingen, brought forward clear experimental proof that female flowers, furnished only with pistils, produce seeds freely in the neighbourhood of the male or staminate flowers, but fail to do so when isolated. He distinctly inferred that the anthers are male organs and the pistil the female organ. The claim set up on behalf of Linnæus that he demonstrated, or helped to demonstrate, the sexes of flowering plants has little foundation in fact. To make out such details of the process of fertilisation as the formation of pollen-tubes, the penetration of the ovules and the fusion of nuclei required the improved microscopes of the nineteenth century.

The almost universal presence both in plants and animals of a process of fertilisation is a fact whose physiological meaning we but imperfectly grasp. Modern research has shown that the pollen-tube is exceptional and confined to the flowering plants; the motile filament of cryptogams, analogous to the spermatozoon of animals, is no doubt a relatively primitive structure, which gives one of the strongest indications of the common origin of all forms of life.

[6] Ray came at last to believe that fossils were the remains of actual organisms, but he was still much hampered by his theological views.

[7] The second of the two has actually been so treated, but without mention of Perrault's name.

[8] See Krause's Life of Erasmus Darwin.

[9] Grew's Anatomy of Plants, 1682.

[10] Wisdom of God, 1691.

PERIOD III

1741-1789

Characteristics of the Period.

The chief historical events are the decline of the French monarchy, the French revolution, the rise of Prussia, the expansion of England, and the American Declaration of Independence. In the history of thought we remark the introduction of the historical or comparative method, which seeks to co-ordinate facts and to trace events to their causes. Science steadily grows in influence, and freethought wins many triumphs; this is the age of Voltaire, Rousseau, and the Encyclopædists, of David Hume, of the French economists and Adam Smith.

Systems of Flowering Plants: Linnæus and the Jussieus.

Linnæus is remembered as a man of great industry, enterprise, and sagacity, who was inspired from boyhood by a passion for natural history and spent a long life in advancing it. He was early recognised as a leader in more than one branch of the study.

L'Obel, Morison, and Ray had laboured to found a natural system of flowering plants, and it was they who laid the foundation upon which all their successors have built. The work did not, however, go steadily forward on the original plan. When Linnæus entered upon the scene the prevalent systems were only moderately natural, and far from convenient in practice. To place the undescribed species which poured in from North America and other distant countries was a difficult task, with which the universities and botanic gardens of Europe could but imperfectly cope. Linnæus, who had the instincts of a man of business, saw that botany was falling into confusion, and that the only remedy was a quick and easy method, which could be mastered in a few days and applied with certainty. No such method, he well knew, could take into account all the intricate affinities of plants, but to devise a perfect method required the labours of generations of botanists; meanwhile a temporary expedient, full of faults it might be, would remove a pressing evil. Flowering plants had been arranged by the divisions of the ovary, or by the petals and sepals, with no very satisfactory results; it occurred to Linnæus to try the number of the stamens and styles. Any such method was bound to present many anomalies, associating plants which are only distantly related, and separating plants which are closely related; but some of the worst anomalies were avoided and some well-established families (Crucifers, Composites, Labiates) retained at the expense of symmetry. Not even the pressing need of simple definitions, which was allowed to spoil so natural a group as the Umbellifers,[11] could induce Linnæus to place Ranunculus and Potentilla in the same class.

Linnæus gained currency for his system by connecting it with the newly accepted doctrine of sexes in plants. That doctrine was not conceived nor demonstrated by him (see p. 48), and it had, as we now see, no further connection with classification by stamens and styles than that it explained the almost universal occurrence of such parts in flowering plants. But Linnæus had persuaded himself that he had done more to establish the existence of sexes in plants than anybody else, and that the physiological importance of stamens and styles was a proof of their systematic value. Neither of these beliefs can stand inquiry, but both were extremely influential on contemporary opinion. The so-called Sexual System achieved an immense success everywhere but in France and Germany. Botanists of small experience were now able to say whether the plants which seemed to be new were really undescribed or not; if undescribed, what was their appropriate place in the system. The congestion of systematic botany was relieved.

The great naturalist appealed to posterity by publishing the sketch of a natural system of flowering plants, which he accompanied by judicious expositions of the philosophy of classification. He had the permanent reform of systematic botany really at heart; he did not believe that his own Sexual System could be final; and he was glad to help in setting up a better one. To this end he united groups of genera into families which he did not pretend to define, being often guided only by an obscure sense of natural bonds of union. Bernard de Jussieu, one of the most patient and observant of systematists, devoted his life to the same task, and profited by the example of Linnæus. He published nothing, but found expression for his views in the arrangement of a botanic garden at Versailles. His ideas were afterwards developed by his nephew, A. L. de Jussieu, in the Genera Plantarum (1789).

Affinity became at length the avowed basis of every botanical system. No convenience in practice, no agreement or difference in habit, was knowingly permitted to override this mysterious property. What then is affinity? What are natural groups of animals and plants, and how do they arise? Until the year 1859 no one could tell. The terse maxims of Linnæus helped to guide naturalists into the right road, but a single fact shows how inadequate they were. Linnæus emphatically and repeatedly declared his belief in the constancy of species. But if species were really constant, affinity between species must have been no more than a delusive metaphor; the resemblances between distinct species could not, on that supposition, be the effect of inheritance.

Linnæus' imperfect appreciation of the fundamental difference between a natural classification of living things and such classifications as man makes for his own practical ends is further revealed by his admission of a third kingdom of nature.[12] Not only animals and plants, but rocks and minerals as well, had, he thought, their genera and species. The genus and species thereby become mere logical terms, independent of inheritance and of life itself.

Linnæus had a passionate love of order and clearness, enforced by an inexhaustible power of work. Hence he was able to serve his own generation with great effect, to methodise the labours of naturalists, to devise useful expedients for lightening their toil (such as his strict binomial nomenclature),[13] and to apply scientific knowledge to the practical purposes of life. But the complexity of nature is not to be suddenly and forcibly reduced to order, and much of Linnæus' work had to be done over again in a different spirit. Cuvier furnishes a somewhat parallel case. Cuvier too was an indomitable worker. His power of organisation moved the wonder of Napoleon, and there has been no greater master of clear thought and clear expression. But, like Linnæus, Cuvier overlooked much that was already obscurely felt and clumsily worded by brooding philosophers, germs of thought which were destined to become all-powerful in the course of a generation or two. It must not be supposed that the labours of Linnæus and Cuvier were bestowed in vain. All that was really valuable in their writings has been saved, and biology will never forget how much it owes to their life-long exertions.

[Carl von Linnécute; (Carolus Linnæus).]

From an engraving (1779) after the portrait by Roslin.

Réaumur and the History of Insects.

Réaumur was born to wealth, and made timely use of his leisure to study the sciences and win for himself a place among natural philosophers. His inclinations directed him first towards mathematics, physics, and, a little later, towards the practical arts. He took a leading part in a magnificent description of French industries, which had been undertaken by the Académie des Sciences. Not content with describing the processes in use, he perpetually laboured to improve them. The manufacture of steel, tin-plate, and porcelain, the hanging of carriages and the fitting of axles, the improvement of the thermometer, glass hives, and the hatching of fowls' eggs by artificial heat are among the many objects to which his attention was directed. Natural History gradually took a more and more prominent place in his studies, and a great History of Insects engaged the last years of his busy life.

Réaumur was neither an anatomist nor a systematist, at least he gained no distinction in either of these branches of biology. No biological laboratory had been dreamt of in his day; he lacked the manipulative skill of Swammerdam or Lyonet; he was no draughtsman, and had to engage artists to draw for him. One qualification of the first importance, however, he possessed in a high degree, the scientific mind. As he watched the acts of an insect, questions at once sagacious and practical suggested themselves in abundance, and these questions he set himself to answer in the best possible way—viz., by observation and experiment. In close attention to the activities of living things his ingenuity and patience found a boundless sphere of exercise. Moreover all that he had seen he could relate in a simple but picturesque manner, using the language familiar to the best French society in the generation next after Madame de Sévigné. Diffuse but clear, amusing but never frivolous, he won and kept the attention of a multitude of readers, the best of whom were incited to adopt his methods or to pursue inquiries which he had indicated. His greatest successes were won in observing and interpreting the natural contrivances of insects, the means by which they get their food and provide for their safety; their transformations, instincts, and societies. Kirby and Spence, which is still one of the best popular accounts of insects in English, is largely based upon Réaumur; so are other well-known treatises, in which the debt is less frankly acknowledged. Réaumur greatly enlarged the knowledge of all kinds of insects except the beetles and Orthoptera, which he did not live to describe, and to this day his Histoire des Insectes is a work of fundamental importance, with which every investigator of life-histories is bound to make himself acquainted.

No abstract of Réaumur's Histoire des Insectes is possible, but we may at least give one example of his mode of treatment. Let us select his account of the proboscis of a moth, the first full account that was ever given. He tells us that all moths have not an effective proboscis, though he does not explain how some of them can dispense with what seems so necessary an organ; this omission has been made good by later entomologists. The proboscis, he goes on, springs from the head, just between the compound eyes. When at rest, it takes up very little room, for it is spirally rolled, like a watch spring; in some cases it makes as few as one and a half or two turns, in others as many as eight or ten; the base is often concealed by a pair of hairy palps, which serve as feelers. Careful study of a moth as she flits from flower to flower shows that she alights on the plant, unrolls her proboscis, passes it into the corolla, withdraws it, perhaps coils it for an instant, and then plunges it again into the tube. When this manœuvre has been repeated several times, the moth flies off to another flower.

Some moths have a tape-like proboscis; in others it is cylindrical. It can be made to protrude by gentle pressure on the head, or be unrolled by a pin passed into the centre of the spire; it is composed of innumerable joints, and tapers from the base to the tip. When forcibly unrolled, it often splits lengthwise into halves. At the time of escape from the chrysalis the halves are always free, and they require careful adjustment in order that a continuous sucking-tube may be obtained. A newly emerged moth may be seen to roll and unroll its proboscis repeatedly, until at last the halves cohere in the proper position. Sometimes they begin to dry before the operation is completed, the half-tubes get curled, and then the unfortunate moth becomes incapable of feeding at all. Each half is a demi-canal, whose meeting edges interlock by minute hooks. The mechanism reminds Réaumur of that which connects the barbs of a feather; in both cases the hooks can be adjusted rapidly and completely by stroking from base to tip, and in both a water-tight junction is obtained. Besides the central canal, along which fluids are sucked up, there are lateral canals (tracheæ) filled with air.

Réaumur was careful to correct his anatomical studies by close observation of the live insect. He reared an angle-shades moth, which he kept several days without food. When he saw it repeatedly extending its proboscis, he put near it a piece of sugar. The moth at once began to suck, and became so absorbed in satisfying its hunger that it allowed Réaumur to carry it on a sheet of paper to a window and to examine it closely with a lens. The proboscis was sometimes extended for several minutes at a time, and then rolled up for an instant; its tip was either employed in exploring the surface or closely applied to the sugar. By means of the lens a slender column of liquid was seen to pass along the central canal towards the head. Now and then, however, a limpid fluid was seen to pass down the proboscis; this was the saliva which was used to moisten the sugar, and then sucked up again.

The Budding-out of New Animals (Hydra): another Form of Propagation without Mating (Aphids).

In the year 1744 a young Genevese, Abraham Trembley, tutor in the family of Bentinck, who was then English resident at the Hague, rose into sudden fame by a solid and well-timed contribution to natural history. Trembley and his pupils used to fish for aquatic insects in the ponds belonging to the residence, and in the summer of 1740 he happened to collect some water-weeds, which he put into a glass vessel and set in a window. When the floating objects had come to rest, a small green stalk, barely visible to the naked eye, was found attached to one of the plants. From one end of the stalk filaments or tentacles were seen to project, and these moved slowly about. When the vessel was shaken the stalk and tentacles contracted, but soon extended themselves again. Was this object a plant or an animal? Its shape and colour were those of a plant, and sensitive plants were known which drooped when touched or shaken. Further observation showed that it could move from place to place, which favoured the animal interpretation. Trembley determined to cut the stalk in two; if the halves lived when separated the fact would favour the plant-theory. The halves at first gave no signs of life beyond occasional contraction and expansion, but after eight days small prominences were seen on the cut end of the basal half. Next day the prominences had lengthened; on the eleventh day they seemed to be growing into tentacles. Before long eight fully formed tentacles were visible, and Trembley had two complete specimens in place of one; both were able to move about.

After four years of observation a handsome quarto volume was published, which told the history of "The freshwater Polyp," a name suggested by Réaumur; the Latin name of Hydra was given by Linnæus. Hydra had been discovered and slightly described forty years before by Leeuwenhoek, who had seen two young polyps branching from one parent and spontaneously becoming free. Trembley made out all that a simple lens, guided by a skilful hand and a keen eye, could discover. Thirteen plates were admirably engraved by another amateur, Pierre Lyonet, who was in all respects a fit companion for Trembley. It was proved that Hydra preyed upon living animals, especially upon the Daphnia or water-flea. When it was well nourished it branched spontaneously again and again, forming a compound mass made up of scores or even hundreds of polyps, all connected with a single base. The power of locomotion and the power of devouring prey were held to settle the animal nature of Hydra, a decision to which zoologists have ever since adhered. Lyonet went on to try the effect of division upon some common freshwater worms, and found that each part grew into a complete worm. Artificial division is not indispensable; in the worm called Nais division takes place spontaneously at certain seasons, one segment dividing repeatedly, so as to form the segments of a complete new individual. The process may be repeated until a chain of worms is produced, which at length breaks up.[14]

A nail was thus driven in a sure place. The conception of an animal was enlarged, for it was shown that an animal may branch and multiply in a way hitherto supposed to be peculiar to plants. The old connecting links between animals and plants (zoophytes, sponges, etc.) had never been really investigated; no one knew what sort of organisms formed or inhabited their plant-like skeletons. But Hydra, thanks to Trembley's description, furnished a clear example of an animal which possessed some of the attributes of a plant. Forms more ambiguous than Hydra, such as Volvox and Euglæna, were ultimately to make the distinction between animal and plant very uncertain and shadowy. It was Hydra that gave the first clue to the structure of the zoophytes, and dispelled the false notion that corals are plants, bearing flowers, fruits, and seeds.

Baer[15] has remarked that Trembley's discovery appreciably modified the teaching of physiology by showing that an animal without head, nerves, sense-organs, muscles, or blood may perceive, feed, grow, and move about.

At the time when Trembley was demonstrating the asexual propagation of Hydra, Bonnet (supra, p. 45) was demonstrating the asexual propagation of aphids. Both naturalists were natives of Geneva, and both, as well as their associate Lyonet, were in a sense pupils of Réaumur, who not only set them an admirable example, but directed their attention to promising researches and discussed with them the conclusions which might be drawn. Réaumur's experience had seemed to confirm Leeuwenhoek's statement (supra, p. 34) that aphids produce young alive, even though no males are to be found among them; but unlucky accidents defeated his intention to confirm it by experiment, and when Bonnet asked him to suggest a piece of work Réaumur gave him the aphid problem.[16]

Bonnet filled a flower-pot with moist earth, introduced a food-plant together with a single new-born aphid, and covered all up with a bell-jar. In twelve days the aphid produced its first young one; in a month ninety-five had been born from the same unfertilised parent. As many as five generations were obtained without the intervention of a male, each successive parent having been isolated from the moment of its birth. It was, however, discovered, apparently by Lyonet, that though viviparous reproduction without males went on regularly so long as food was plentiful, males appeared towards the end of summer, and fertilised the eggs which were destined to outlast the winter.

The aphids added a new and peculiar example to the known cases of asexual propagation (plants and Hydra). Much discussion followed, but the physiology of that age (and the same is true of the physiology of our own age) was unable to reveal the full significance of the observed facts. Insects have since furnished many instances of unfertilised eggs which yield offspring. One such instance was already recorded, though neither Leeuwenhoek, Réaumur, nor Bonnet knew of it. In the year 1701 Albrecht of Hildesheim placed a pupa in a glass vessel and forgot it. A moth hatched out and laid eggs, from which a number of caterpillars issued.

Lyonet, whom we have more than once had occasion to mention, afterwards became celebrated as the author of one of the most laborious and beautiful of insect-monographs. The structure of the larva of the goat-moth was depicted by him in eighteen quarto plates, crowded with detail.

The Historical or Comparative Method: Montesquieu and Buffon.

About the middle of the eighteenth century we remark the introduction of a new, or almost new, method of investigation, which was destined to achieve great results. Hitherto many men had been sanguine enough to believe that they could think out or decide by argument hard questions respecting the origin of what they saw about them. It was easier, but not really more promising, to resort to ancient books which contained the speculations of past generations of thinkers. Now at last men set themselves to study what is, and by the help of historical facts to discover how it came to be. The new method was first applied to the institutions of human society, but was in the end extended to the earth, life on the earth, and a multitude of other important subjects.

Most writers call this method historical, because history is the chief means by which it seeks to trace causes. Others call it genetic, because it goes back, whenever it can, to origins. It might also be called comparative, because it compares, not only things which are widely separated in time, but also things which are separated in space, things which differ in form or tendency because they have a common origin, and things which differ in origin because they have a common form or tendency. Whether the institutions, arts, and usages of mankind, or the species of plants and animals, are in question, the study of history, together with the comparative study of what now exists, results in increased attention to development, and this again brings to light the continuity of all natural agents and processes—continuity in time and continuity among co-existences. Since the new method has succeeded in tracing the causes of many phenomena which once seemed to obey no law, it has done much to strengthen the belief in universal causation.

Down to the middle of the eighteenth century the book of Genesis had been almost unanimously accepted in Europe as the only source of information concerning the origin of the world, of man, of languages, of arts and sciences. The whole duration of the world was restricted to so brief a space that slow development was impossible, and it was assumed that early history of every kind must be miraculous.[17]

Montesquieu (Esprit des Lois, 1748) was the first to exhibit on an impressive scale the power of the historical method. Natural development, determined by unalterable conditions, was with him the key to the right understanding of the past. It is well known that here and there a great thinker had before Montesquieu framed something like the same conception. The Politics of Aristotle[18] and Vico's study of the historical evolution of the Roman law (1725) are memorable anticipations. By 1748, the date of the Esprit des Lois, or 1749, the date of Buffon's first volumes, which come next before us, Newton's Principia had made students of physics and astronomy practically familiar with the notion of universal causation.

Buffon's place in the history of science is that of one who accomplished great things in spite of weaknesses peculiarly alien to the scientific spirit. It was mainly he who, by strenuous exertions and largely at his own cost, transformed the gardens from which the king's physicians used to procure their drugs into what we now know as the Jardin des Plantes. By the untiring labours of fifty years he produced a Natural History in thirty-six volumes crowded with plates. Having won for himself a place side by side with Montesquieu and Gibbon, he employed it to direct attention to the larger questions of biology and geology. He was a pronounced freethinker, who promulgated bold views with a dexterity which saved him from condemnation by the theological tribunals. When his opinions were declared to be contrary to the teaching of the Church, he printed a conciliatory explanation, but never cancelled the passages objected to, which continued to appear in a succession of editions. His deficiencies, we must admit, were serious. He was a poor observer (partly because of short sight), and had no memory for small details. His enemies were able to taunt him with absurd mistakes, such as that cows shed their horns. He alienated the two foremost naturalists of the eighteenth century, Linnæus and Réaumur, by ignorant and scornful criticisms. His strong propensity to speculation, insufficiently checked by care to verify, might have brought him under the sarcastic remark of Fontenelle, that ignorance is less apparent when it fails to explain what is, than when it undertakes to explain what is not.

Buffon's fame is not seriously impaired by the fact that his great work is no longer read except by those who study the course of scientific thought. Few productions of the human intellect retain their value after a hundred years, and scientific treatises become obsolete sooner than others. It is consoling to recollect that, if their energy is quickly dissipated, it is at least converted into light.

In a history of biology Buffon is naturally a more important figure than Montesquieu. Buffon had imbibed evolutionary views from the Protogæa of Leibnitz, which in turn made use of certain hypotheses of Descartes.[19] The Histoire Naturelle inclines to some theory of evolution, especially in the later volumes. At first Buffon teaches that species are fixed and wholly independent of one another; some years later he is ready to believe that all quadrupeds may be derived from some forty original forms, while in a third and subsequent passage he puts the question whether all vertebrates may not have had a common ancestor. He does not shrink from saying that one general plan of structure pervades the whole animal kingdom—a belief that he could never have adequately supported by facts; Baer long afterwards (1828) searched in vain for evidence on this very point, while Darwin in 1859 admitted that his arguments and facts only proved common descent for each separate phylum of the animal kingdom;[20] he inferred from analogy that probably all the organic beings which have ever lived on this earth have descended from some one primordial form.[21] Elsewhere Buffon makes bold to declare that Nature in her youthful vigour threw off a number of experimental forms of life, some of which were approved and adopted, while others were allowed to survive in order to give mankind a wider conception of her projects. There is generally some gleam of truth in Buffon's most fantastic speculations, but we often wish that he could have attended to the warning of Bossuet: "Le plus grand dérèglement de l'esprit est de croire les choses parce qu'on veut qu'elles soient."

[Georges Louis Leclerc, Comte de Buffon.]

Against all his shortcomings we must set the fact that Buffon strove to interpret the present by the past, the past by the present, geology by astronomy, geographical distribution by the physical history of the continents. One of his maxims expresses the fundamental thought of Lyell's Principles of Geology: "Pour juger de ce qui est arrivé, et même de ce qui arrivera, nous n'avons qu'à examiner ce qui arrive."

Hard-and-fast distinctions are the marks of imperfect theory. Early philosophers distinguished hot and cold, wet and dry, light and dark, male and female, as things different in kind. In later times organic and inorganic, animal and vegetable, the activities of matter and the activities of mind, have been sharply separated. But as knowledge increases these distinctions melt away; it is perceived that the extreme cases are either now connected by insensible gradations, or else spring historically from a common root. Hutton, Lyell, and their successors have made it clear that the history of the earth calls for no agents and no assumptions beyond those that are involved in changes now going on; the present is heir by unbroken descent to the past. Continuity has been established between all forms of energy. Even the chemical elements, once the emblems of independence, give indications that they too had a common origin. The nebular hypothesis, which has been steadily rendered more probable by the scientific discoveries of two centuries, traces all that can be perceived by the senses to a homogeneous vapour, and lays the burden of proof on those who believe that continuity has its limits. Every history, whether of planetary systems, or of the earth's crust, or of human civilisations, religions, and arts, is recognised as a continuous development with progressive differentiation.

Amateur Students of Living Animals.

A history of biology would be incomplete which took no notice of every-day observations of the commonest forms of life. Some of the best are due to the curiosity of men with whom natural history was no more than an occasional recreation. William Turner (a preacher, who became Dean of Wells), Charles Butler (a schoolmaster), Caius and Lister (physicians), Claude Perrault (a physician and architect), Méry and Poupart (surgeons), Frisch (a schoolmaster and philologue), Lyonet (an interpreter and confidential secretary), Roesel (a miniature painter), Henry Baker (a bookseller, who gained a competence by instructing deaf mutes), Leroy (ranger to the King of France), Stephen Hales, Gilbert White and William Kirby (country parsons), and William Spence (a drysalter) were all amateurs in natural history. To this list we might add Willughby, Ray, Leeuwenhoek, Réaumur, De Geer, Buffon, the Hubers, and George Montagu, who were either so fortunate in their worldly circumstances or so devoted to science as to make it their chief, or even their sole pursuit, though they did not look to it for bread. A large proportion of the naturalists whose names have been quoted occupied themselves with the habits and instincts of animals, and biology has been notably enriched by their observations. To Englishmen the most familiar name is that of Gilbert White, in whom were combined thirst for knowledge, exactness in description, and a feeling for the poetry of nature.

White used his influence to encourage what may be called live natural history, which, as he understood it, "abounds in anecdote[22] and circumstance." He bids his correspondents to "learn as much as possible the manners of animals; they are worth a ream of descriptions." His example has done more than his exhortations. He focusses a keen eye upon any new or little-known animal, such as the noctule, the harvest-mouse, or the mole-cricket; detects natural contrivances little, if at all, noticed before, such as the protective resemblance of the stone-curlew's young; dwells upon the practical applications of natural history, such as the action of earthworms in promoting the fertility of soils; and combines facts which a dull man would be careful to put into separate pigeon-holes, such as the different ways in which a squirrel, a field-mouse, and a nuthatch extract the kernels of hazel-nuts.

The many amateurs of the eighteenth century naturally demanded books written to suit them, and illustrated books with coloured plates, coming out in parts, found a ready sale. Some were devoted to insects, others to microscopic objects. In accordance with prevalent belief, the writers made a point of tracing the hand of Providence in the minutest organisms; many popular treatises were altogether devoted to natural theology. Some few of these natural history miscellanies contained original work, which has not yet lost its interest. The best is Roesel's Insecten-belustigungen (four vols. 4to., 1746-61), memorable among other things for containing the original description of Amœba. For English readers Henry Baker wrote The Microscope Made Easy (1743) and Employment for the Microscope (1753).

Intelligence and Instinct in the Lower Animals.

The period with which we are now concerned (1741-1789) initiated the profitable discussion of the mental powers of animals. We are unable for lack of space to follow the investigation from period to period, and must condense into one short section whatever its history suggests.

In the year 1660 Aristotelians were still discoursing about the vegetative and sensitive souls which bridged the gulf between inanimate matter and the thinking man. Descartes had tried to prove that the bodies of men and animals are machines actuated by springs like watches. Man, however, according to Descartes, possesses a soul wholly different in its properties from his body, and apparently incapable of being acted upon by it. Man only can think; animals are capable only of physical sensations, and have no consciousness. Into speculations like these we shall not venture, being- content, like Locke, "to sit down in quiet ignorance of those things which upon examination are proved to be beyond the reach of our capacities." We shall merely note here and there facts ascertained by observation or experiment, and plain inferences drawn from such facts.

Swammerdam and Réaumur, besides many naturalists of less eminence, recorded a host of observations on the activities of insects. They contributed little to the discussion except new facts, for habit led them to ascribe without reflection every contrivance to the hand of Providence or else to Nature. Some of their facts, however, made a deep impression, none more than the exact agreement of the cells of the honeycomb with the form which calculation showed to be most advantageous.[23] The coincidence has lost some of its interest since the discovery that the theoretically best form of cell is hardly ever realised.[24] Réaumur,[25] in describing the process by which a certain leaf-eating caterpillar makes a case for itself out of the epidermis of an elm-leaf, showed that the caterpillar is not devoid of that kind of intelligence which adapts measures to circumstances. He cut off the margin where the upper epidermis of the leaf passes into the lower one, a margin which the insect had intended to convert into one side of its case; the caterpillar sewed up the gap. He cut off a projection which was meant to form part of the triangular end of the case; the caterpillar altered its plan, and made that the head-end which was originally intended to lodge the tail. This observation anticipates a better-known example taken from the economy of the hive-bee by Pierre Huber, which is mentioned below.

Buffon[26] heard with impatience all expressions of admiration for the works of insects. His poor eyesight and his repugnance to minutiæ disinclined him to pay much attention to creatures so small, and he had set himself up as the rival of Réaumur in physics and natural history. To pour contempt upon insects gratified both feelings at once. Bees, he said, show no intelligence at all; their actions are purely automatic, and their much-vaunted architecture is merely the result of working in a crowd. The cells of the honeycomb are hexagonal, not by reason of forethought or contrivance, but because of mutual pressure; soaked peas in a confined space form hexagonal surfaces wherever they touch.

The elder Huber seems to have denied to bees every trace of intelligence, but his son Pierre found it hard to go so far.[27] He remarked that the storage-cells of a honeycomb are not always exactly alike; they may be lengthened, cut down, or curved, when requisite. Cells which had been rudely trimmed with a knife were repaired with such dexterity and concert as to suggest that even the hive-bee has "le droit de penser." Bees would under compulsion build upwards or sideways, instead of downwards, as they like to do. Finding that they sought to extend their combs in the direction of the nearest support, he covered the support with a sheet of glass, on which they could get no footing. They swerved at once from the straight line, and prolonged their comb towards the nearest uncovered surface, though this obliged them to distort their cells. He was driven to the conclusion that bees possess "a little dose of judgment or reason." In our own time, when all conscious adaptation of means to ends is believed to be worthy of the name of reason, it requires no great courage to ask why we deny such an attribute to all the lower animals.

In spite of examples like this, the favourite expression "blind instinct" helped to strengthen the conviction that the mental processes of animals are unsearchable. It is impossible to deny that the epithet blind is appropriate in many cases. A bird will sit an addled egg all summer, or vainly but repeatedly attempt to make its tunnel in the insufficient breadth of a mud wall (Geositta). Of course such instances do not show that all the acts of the lower animals are devoid of intelligence.

Hume in 1739 and again in 1748 appealed to everyday observation of dogs, birds, and other animals of high grade. The facts seemed to him to show that animals as well as men are endowed with reason and able to draw inferences; he did not, however, credit them with the power of framing general statements, holding that experience operates on them, as on children and the generality of mankind, by "custom" alone. It is notorious that the dog and other higher animals learn by experience; Hume tells, for instance, how an old greyhound will leave the more fatiguing part of the chase to younger dogs, and place himself so as to meet the hare in her doubles. On the other hand (though Hume does not say so) man himself possesses non-educable instincts. In short, Hume sees no ground for drawing a line between the mental powers of man and those of the higher animals, though he attributes to man a power of demonstrative reasoning to which animals do not attain. In this he substantially agrees with Aristotle,[28] who maintained that in animals the germs of the psychical qualities of the man are evident, though, as in the child, they are undeveloped. Hume's teaching also accords with modern views; comparative anatomy, for instance, "is easily able to show that, physically, man is but the last term of a long series of forms, which lead by slow gradations from the highest mammal to the almost formless speck of living protoplasm, which lies on the shadowy boundary between animal and vegetable life."[29]

The detailed proofs which Hume was not enough of a naturalist to furnish were at length stated with admirable clearness and force by Leroy, whose Letters on Animals form the most important contribution made to the discussion during our period. Georges Leroy (1723-1789) was lieutenant des chasses under the last French kings, and had charge of the parks at Versailles and Marly. He wrote therefore with knowledge about the wolf, fox, deer, rabbit, and dog. His pages are enlivened by many touches of nature, interesting to readers who perhaps care little about psychology. Leroy attributes to the wolf observation, comparison, judgment. The wolf must mark the height of the fold which encloses a flock, and judge whether he can clear it with a sheep in his mouth. Wolf and she-wolf co-operate artfully in the running-down of prey. Sometimes the she-wolf will draw off the sheep-dog in pursuit, thus putting the flock at the mercy of her mate. Or one of the two will chase the quarry till it is out of breath, when the other can take up the running on advantageous terms. An old fox shows knowledge of the properties of traps, and will rather make a new outlet or suffer long famine than encounter them. But when he finds a rabbit already caught, he realises that the trap has lost its power to hurt. Sheep-dogs can be educated to mind things which do not interest wild dogs, or dogs of other breeds; when, for instance, the flock is driven past a patch of wheat, the dog in charge will take care that the sheep do not damage the crop. A trained sporting-dog learns at length to trust his own judgment, even in opposition to that of his master, and sportsmen know that they must direct young dogs, but leave old ones to act for themselves.

From the middle of the eighteenth century to the present day naturalists and psychologists have been labouring to distinguish instinct from intelligence. It is not hard to define well-marked examples of each, and to show that a typical instinct is congenital (not the result of a process of education or self-education), adaptive (conducive to the welfare of the organism), co-ordinated by nerve-centres (thus excluding the superficially similar behaviour of the lowest animals and all plants), actuating the whole organism (thus excluding most, if not all, reflex acts in the higher animals, as well as the wonderful adjustments effected by bone-corpuscles and other parts of organisms), and common to all the members of a species or other group (thus excluding individual aptitudes).[30] In the same way it is easy to point out clear differences between a bird and a tree. But just as a definition which shall separate every animal from every plant has hitherto been sought in vain, so it has hitherto been impossible to frame a definition which while including all instincts shall admit no case of reflex action or intelligence. The most ambiguous cases of all are perhaps to be found in insects, where, as will shortly be explained, our information is ill-fitted to support precise distinctions.

Many naturalists entertain some form of what may be called the use-and-disuse or inherited-memory theory, supposing that the aptitudes of the offspring are influenced by the activities of the parent. Some cling to the belief that habits can be fixed and transmitted, and we must admit that the fixation and transmission of habits might explain a great deal. But all the evidence goes to prove that habits are not inherited at all, and that we must look elsewhere for the origin of instincts. Let naturalists who think differently try to account for the instincts of working bees or ants, which receive their psychical not less than their physical endowment from a long succession of ancestors, none of which worked for their living. Or let them try to explain the instances of spiders, insects, etc., which after egg-laying practise instinctive arts for the defence of their brood, standing over the eggs, carrying them about, blocking the entrance of the burrow, etc. May we not say that it is impossible for the acts of a parent to influence the congenital instincts of offspring which have already lost connection with the mother? But surely a theory of instinct breaks down which fails to account for the expedients by which the worker-bee, the worker-ant, and the spider provide for the safety of the unhatched brood or for the welfare of the community.

Darwin's Origin of Species threw a new light upon instinct by showing that natural selection can operate on the subtlest modifications. It can discriminate shades of hardiness to climate, shades of intellectual acuteness, or shades of courage. It can intensify qualities which appear only in adults past bearing or in individuals congenitally incapable of propagation. Human selection, though a blunt tool in comparison with natural selection, can originate a bold and hardy race of dogs, or showy double flowers incapable of producing seed. In the second case fertile single flowers continue the race, as in the garden Stock. Darwin pointed out that the barren double flowers of the Stock answer to the workers of social bees and ants, the fertile single flowers to the functional males and females. Every modification that works to the advantage or disadvantage of the race, whether we classify it as physical, intellectual, or moral, gives scope for the operation of natural selection.

The comparative psychology of small invertebrates, such as insects, is impeded by our imperfect knowledge of their nervous physiology. Introspection is here impossible; experimental physiology and pathology, which have done so much for the psychology of the higher vertebrates, almost impossible; analogy is a treacherous guide where the structures involved differ conspicuously. We have little to guide us in the psychology of insects except their behaviour, and that is often capable of a variety of interpretations. The only course is to adopt Pasteur's watchword, "Travaillons!"—the difficulties will diminish with time and labour.

The Food of Green Plants.

Common observation taught men in very early times that green plants draw nourishment from the soil, and that sunlight is necessary to their health. In the age of Galileo a Belgian physician and chemist, Van Helmont, endeavoured to pursue the subject by experiment. He planted the stem of a live willow in furnace-dried earth, which was enclosed in an earthen vessel. Rain-water or distilled water was supplied when necessary, and dust excluded by a perforated lid. The loss of weight due to the falling-off of leaves was neglected. In the course of five years the tree was found to have increased to more than thirty times its original weight; Van Helmont concluded that this increase was due to water only. Malpighi (1671), being guided mainly by his microscopic studies of the anatomy of the stem and leaf, taught that moisture absorbed by the roots ascends by the wood, becoming (apparently at the same time) aerated by the large, air-conducting vessels; that it enters the leaves, and is there elaborated by evaporation, the action of the sun's rays, and a process of fermentation; lastly, that the elaborated sap passes from the leaves in all directions towards the growing parts. It will be seen that this explanation, though incomplete, makes a fair approximation to the beliefs now held; for more than a hundred years after Malpighi's day less instructed opinions were commonly held. Hales (1727) recognised that green plants are largely nourished at the expense of the atmosphere; he dwelt also on the action of the leaves in drawing water from the soil, and in discharging superfluous moisture by evaporation.

Joseph Priestley, who had been proving that air is necessary both to combustion and respiration, made an experiment in 1771 to discover whether plants affected air in the same way that animals do. He put a sprig of mint into a vessel filled with air in which a candle had burned out, and after ten days found that a candle would now burn perfectly well in the same air. Air kept without a plant, in a glass vessel immersed in water, did not regain its power of supporting combustion. Balm, groundsel, and spinach were found to answer just as well as mint. Air vitiated by the respiration of mice was restored by green plants as readily as air which had been vitiated by combustion.

Priestley did not remark that the glass vessels employed in his experiments had been set in a window, and inattention to this point caused some of his attempts to repeat the experiment to fail. He was further perplexed by using vessels which had become coated with a film of "green matter," probably Euglæna. Such vessels restored vitiated air, though no leaves were present, and when placed in the sun, gave off considerable quantities of a gas, Priestley's "dephlogisticated air" (oxygen). Hardly any oxygen was given off when the green matter was screened by brown paper. Water impregnated with carbonic acid was found to favour the production of the green matter. To us, who have been taught at school something about the properties of green plant-tissues, it seems obvious that Priestley ought to have ascertained by microscopic examination whether his "green matter" was not a living plant. But he had always avoided the use of the microscope, his eyes being weak, and after some imperfect attempts in this way he made up his mind that the green matter was neither animal nor vegetable, but a thing sui generis. Neglecting his most instructive experiments, and not waiting till he could devise new ones, or even disentangle his thoughts, he sent to the press a confused explanation, which seemed to teach that vitiated air may be restored by sunlight alone.

A Dutch physician, named John Ingenhousz, who was then living in England, read Priestley's narrative and began to investigate on his own account. Without detailing his numerous experiments, we may give his own clear summary (condensed). "I observed," Ingenhousz says, "that plants have a faculty to correct bad air in a few hours; that this wonderful operation is due to the light of the sun; that it is more or less brisk according to the brightness of the light; that only the green parts of the plant can effect the change; that leaves pour out the greatest quantity of oxygen from their under surfaces; that the sun by itself has no power to change the composition of air." It will be seen that Priestley started the inquiry, devised and executed the most necessary experiments, and got excellent results. Then he lost his way, and bewildered by conflicting observations, which he was too impatient to reconcile, published a barren and misleading conclusion. Nothing was left for him but to acknowledge that Ingenhousz had cleared up all his perplexities.

Nicholas Theodore de Saussure, son of the Alpine explorer, showed in 1804 that when carbon is separated from the carbonic acid of the air by green plants, the elements of water are also assimilated, a result which owes its importance to the fact that starch is a combination of carbon with the elements of water. Saussure also proved that salts derived from the soil are essential ingredients of plant-food, and that green plants are unable to fix the free nitrogen of the air; all the nitrogen which they require is obtained from the ground.

We are unable to follow the history further. Though the main facts were established as early as the beginning of the nineteenth century, experimental results of scientific and practical interest have never ceased to accumulate down to the present time.

The Metamorphoses of Plants.

Speculations concerning the nature of the flower roused at one time an interest far beyond that felt in most botanical questions. The literary eminence of Goethe, who took a leading part in the discussion, heightened the excitement, and to this day often prompts the inquiry: What does modern science think of the Metamorphoses of Plants?

Let us first briefly notice some anticipations of Goethe's famous essay. In the last years of the sixteenth century Cesalpini, taking a hint from Aristotle, tried to establish a relation between certain parts of the flower and the component layers of the stem. Linnæus worked out the same notion more elaborately, and with a confidence which sought little aid from evidence. His wonderful theory of Prolepsis (Anticipation) need not be described, far less discussed, here. He also borrowed and adapted an analogy which had been thrown out by Swammerdam. The bark of a tree, which according to the theory of Prolepsis gives rise to the calyx of the flower, he compared to the skin of a caterpillar, the expansion of the calyx to the casting of the skin, and the act of flowering to the metamorphosis by which the caterpillar is converted into a moth or butterfly. More rational than the speculations just cited, and more suggestive to the morphologists of the future, are his words: "Principium florum et foliorum idem est" (Flower and leaf have a common origin)—which was not, however, a very novel remark in the eighteenth century. Long before Linnæus early botanists had remarked the resemblance of sepals, petals, and seed-leaves to foliage-leaves; Cesalpini has a common name for all (folium).

At the very time when Linnæus was occupied with his fanciful analogies, a young student of medicine named Caspar Friedrich Wolff, who was destined to become a biologist of great note, published a thesis which he called Theoria Generationis (Halle, 1759). This thesis marks an epoch in the history of animal embryology, but what concerns us here is that Wolff examined the growing shoot, and there studied the development of leaf and flower. He found that in early stages foliage-leaves and floral-leaves may be much alike, and thought that he could trace both to a soft or even fluid substance, which is afterwards converted into a mass of cells. It seemed to him possible to resolve the flowering shoot into stem and leaves only. Wolff's thesis, or at least that part of it which dealt with the plant, was little read and soon forgotten; his studies of the development of animals were carried further and became famous.

Goethe in 1790 revived Wolff's theory of the flower, without suspicion that he had been anticipated. It is only our ignorance, he said, when the fact came to his knowledge, that ever deludes us into believing that we have put forth an original view. As soon as he realised the true state of the case, he spared no pains to do Wolff full justice.

The aim of Goethe's Metamorphoses of Plants was to determine the Idea or theoretical conception of the plant, and also to trace the modifications which the Idea undergoes in nature. These two inquiries constituted what he called the Morphology of the plant, a useful, nay, indispensable term, which is still in daily use. He thought that he could discover in the endless variety of the organs of the flowering plant one structure repeated again and again, which gradually attained, as by the steps of a ladder, what he called the crowning purpose of nature—viz., the sexual propagation of the race. This fundamental structure was the leaf. The proposition that all the parts of the flower are modifications of the leaf he defended by three main arguments—viz., (1) the structural similarity of seed-leaves, foliage-leaves, bracts, and floral organs; (2) the existence of transitions between leaves of different kinds; and (3) the occasional retrogression, as he called it, of specially modified parts to a more primitive condition. These lines of argument were illustrated by many well-chosen examples, the result of long and patient observation. Goethe did not, however, fortify his position by the likeness of developing floral organs to developing foliage-leaves, which had been Wolff's starting-point. He arrived independently at Wolff's opinion that the conversion of foliage-leaves into floral organs is due to diminished nutrition.

Linnæus's exposition of the nature of the flower had been read attentively by Goethe, who must have remarked that the conversion of organs to new uses was there described as a metamorphosis. That word had been, long before the time of Linnæus, appropriated to a particular kind of change—viz., an apparently sudden change occurring in the life-history of one and the same animal. It was therefore unlucky that Goethe should have been led by the example of Linnæus to employ the word in the general sense of adaptation to new purposes. He did not, however, expressly compare flower-production with the transformation of an insect, as Linnæus had done.

The reception of Goethe's Metamorphosen der Pflanzen was at first cold, but the doctrine which it enforced gradually won the attention of botanists, and by 1830 he was able to show that it had been accepted by many good judges.

Then came the discoveries of Hofmeister, followed by Darwin's Origin of Species. Naturalists soon ceased to put the old questions, and the old answers did not satisfy them. Wolff and Goethe had generalised the flowering plant until it became a series of leaf-bearing nodes alternating with internodes, but no such abstract conception could throw light upon the common ancestor of all the flowering plants, nor upon the stages by which the flowering plant has been evolved, and it was these which were now sought. Hofmeister brought to light a fundamental identity of structure in the reproductive organs of the flowering plants and the higher cryptogams. There has since been no doubt in what group of plants we must seek the ancestor of the flowering plant. It must have been a cryptogam, not far removed from the ferns, and furnished with sporophylls—i.e., leaf-like scales, on which probably two kinds of sporangia, lodging male and female spores respectively, were borne. The careful investigation of the fossil plants of the coal measures has brought us still nearer to the actual progenitor. Oliver and Scott[31] have pointed out that the carboniferous Lyginodendron, though showing unmistakable affinity with the ferns, bore true seeds, as a pine or a cycad does. Many other plants of the coal measures are known to have combined characteristics of ferns with those of cycads, while some of them, like Lyginodendron, crossed the frontier, and became, though not yet flowering plants, at least seed-bearers.

The discovery of a fossil plant which makes so near an approach to the cryptogamic ancestor of all the flowering plants may remind us how little likely it was that the ideal plant of Wolff and Goethe, consisting of leaves, stem, and other vegetative organs, but without true reproductive organs, should fully represent the type from which the flowering plants sprang. No plant so complex as a fern could maintain itself indefinitely without provision for the fertilisation of the ovum; the only known asexual plants are of low grade, and, it may be, insufficiently understood.

What substratum of plain truth underlies the doctrine of the metamorphoses of plants? Botanists would agree that all sporophylls, however modified, are homologous or answerable parts. Carpels and stamens are no doubt modified sporophylls. Petals are sometimes, perhaps always, modified stamens, and therefore modified sporophylls also. We must not call a sporophyll a leaf, for it contains a sporangium of independent origin, and the sporangium is the more essential of the two. The common origin of foliage-leaf, bract, perianth-leaf, sporophyll (apart from the sporangium), and seed-leaf is unshaken. We may picture to ourselves a plant clothed with nearly similar leaves, some of which either bear sporangia or else lodge sporangia in their axils. Part of such a primitive flowering plant might retain its vegetative function and become a leafy shoot, while another part, bearing crowded sporophylls, might yield male, female, or mixed cones. From an ancestor thus organised any flowering plant might be derived. But the chief wonder of the theory of Metamorphoses—viz., the derivation of stamen and pistil from mere foliage-leaves—disappears. Anther and ovule take their real origin from the sporangium, whose supporting leaf is only an accessory.

The chief steps by which the morphology of the flowering plant has been attained are these:—Cesalpini (1583), followed by several other early botanists, recognized the fundamental identity of foliage-leaf, perianth-leaf, and seed-leaf. Linnæus (1759) added stamen and carpel to the list, identifications of greater interest, but only partially defensible. Wolff (1759) justified by similarity of development the recognition of floral organs as leaves. Goethe (1790) traced structural similarity, transitions, and retrogression in leaves of diverse function. Hofmeister (1849-57) showed a relationship between the flowering plant and the higher cryptogams. Oliver and Scott (1904), inheriting the results of Williamson's work, discovered a carboniferous seed-bearing plant, one of a large group intermediate between ferns and cycads. It is now possible to explain the resemblance of the various leaf-like appendages of the flowering plant by derivation either from the leaves or the sporophylls (the latter not being wholly leaves) of some extinct cryptogam, which was either a fern or a near ally of the ferns.

Early Notions about the Lower Plants.

The fathers of botany neglected everything else in order to concentrate their attention upon the flowering plants, from which very nearly all useful vegetable products were derived. The lack of adequate microscopes rendered it almost impossible to investigate the structure and life-history of ferns, mosses, fungi, and algæ until the nineteenth century. As late as the time of Linnæus it was possible to maintain that they developed spontaneously, though the great naturalist himself called them Cryptogamia, thereby expressing his conviction that they reproduce their kind like other plants, but in a way so far not understood. Gaertner, a contemporary of Linnæus, pointed out one important respect in which the spores of cryptogams differ from the seeds of flowering plants, viz. that they contain no embryo.

Ferns.—Even before the age of Linnæus it was known that little ferns spring up around the old ones, and that a fine dust can be shaken from the brown patches on the back of ripe fern-leaves. The dust was reputed to be the seed of the fern, and in an age which believed in magic the invisibility of fern-seed made it easy to suppose that the possessor of fern-seed would become invisible also. When the microscope began to be applied to minute natural objects, the brown patches of the fern-leaf were closely examined. William Cole of Bristol (1669), Malpighi, Grew, Swammerdam, Leeuwenhoek, and others, found the stalked capsules (sporangia), their elastic ring and the minute bodies (spores) lodged within them; it seemed obvious to call the capsules ovaries and the spores seeds. Some time in the latter part of the seventeenth century Robert Morison, professor of botany at Oxford, who died in 1683, sowed spores of the harts-tongue fern, and next year got an abundant crop of prothalli, which he took to be the cotyledons. A little later, when it had been proved that flowering plants possess male and female organs, diligent search was made for the stamens and pistils of ferns and mosses, which of course could not be found, though identifications, sometimes based upon a real analogy, were continually announced. Late in the eighteenth century one John Lindsay, a surgeon in Jamaica, who was blest with leisure and a good microscope, repeated the experiment of Morison, which seems to have been almost forgotten. Having remarked that after the rains young ferns sprang up in shady places where the earth had been disturbed. it occurred to him to mix the fine brown dust from the back of a fern-leaf with mould, sow the mixture in a flower-pot, and watch daily to see what might come up. About the twelfth day small green protrusions were observed, which enlarged, sent down roots, and formed bilobed scales, out of which young ferns ultimately grew. In 1789 Sir Joseph Banks, who was reputed to be the best English botanist of the day, asked Lindsay's help in sending West Indian ferns to Europe. Lindsay replied that it would be easier to send the seed, and that the seed would grow if properly planted. This was new to Banks, who demanded further information. Lindsay then prepared a short illustrated paper, which Banks communicated to the newly formed Linnean Society. It will be seen that Lindsay was able to add nothing of much importance to what Morison had ascertained a century before. The spores were still identified with seeds, the prothallus was still a cotyledon, and for years to come botanists continued to seek anthers on fern-leaves. At this point we suspend for a time the history of the discovery (see below, p. 108).

Mosses.—Linnæus observed that the large moorland hair-moss (Polytrichum) is of two forms, only one of which bears capsules, and further that in dry weather the capsules emit masses of fine dust. No further progress was made until 1782, when Hedwig, in a memoir of real merit, described the antheridium and archegonium of the moss, and traced the capsule to the archegonium. Interpreting the organs of the moss by those of the flowering plant, he called the antheridia anthers, the capsule was a seed-vessel, the spores were seeds, and the green filament emitted by the germinating spore a cotyledon. Such misinterpretations were then inevitable.

Fungi.—Micheli in 1729 found the spores of several fungi, germinated them, and figured the product. The figures show the much-branched filament (mycelium) which burrows in the soil and constitutes the vegetative part of the fungus, and also here and there a pileus (mushroom, toadstool, &c.), which is the fructification springing out of the mycelium. His account comprises the best part of what is known down to the present time of the reproduction of that group of fungi to which the mushroom belongs.

Algæ.—Some early observers (Réaumur among the rest) studied the enlarged and fleshy branches of brown seaweeds, and discovered the seed-like spores.

This scanty knowledge of the life-history of cryptogams sufficed until the nineteenth century, when the study was resumed with better microscopes and in a far more connected way, with results of the highest interest and importance (see below, p. 108).

[11] By associating with them a number of alien genera.

[12] The third kingdom of nature was taken from the alchemists.