Grew, like Malpighi, derives the young layers of wood in the stem from the innermost layers of the rind. The true wood, he says on page 114, is entirely composed of old lymph-vessels, that is of fibres, which lay originally in the inner circumference of the rind. But by true woody substance he understands the fibrous components of the wood, excluding the air-vessels; his lymph-vessels are the bast-fibres and similar forms; for, he goes on, the air-vessels with the medullary rays and the true wood form what is commonly called the wood of a tree; he uses the term air-vessels, not because these forms never contain sap, but because they only contain a vegetable air during the proper period of vegetation, when the vessels of the rind are filled with sap.
The above is certainly a very imperfect account of Grew’s services to phytotomy; for the points here made prominent were treated by him as accessories only to the coarser histological relations with which he chiefly occupied himself.
These two works of Malpighi and Grew, so important not only for botany but for the whole range of natural science, were not followed during the course of the next hundred and twenty years by a single production, which can claim in any respect to be of equal rank with them; that long time was a period not of progress but of steady retrogression, as we shall see in the next chapter. But before the beginning of the 18th century Anton von Leeuwenhoek[68] made some contributions to the knowledge of the details of vegetable anatomy, if not exactly to the settling of very important points in it; he communicated his observations on animal and vegetable anatomy in numerous letters to the Royal Society of London, and these appeared for the first time in a collected form in Delft in 1695 under the title of ‘Arcana naturae.’ It is not easy to gain a clear idea of Leeuwenhoek’s phytotomic knowledge from his scattered statements. He too discussed the less minute anatomy of fruits, seeds and embryos, and among other things he made occasional observations on germination, and many on the structure of different woods. But all bears the stamp of only occasional study of plants; he was led to his observations by questions of the nature-philosophy then in vogue, and especially by such as were connected with the theory of evolution, not unfrequently by mere curiosity and pleasure in things obscure and inaccessible to ordinary people, but he did not gain from them a general idea of the structure of plants. In the course of these observations he did unquestionable service in perfecting simple magnifying glasses; he made a large number with his own hands, and these possessed magnifying powers evidently not at the command either of Malpighi or Grew. By aid of such glasses he discovered the vessels of secondary wood which are not spirally thickened but beset with pits, the true character of which however he did not investigate. He was the first moreover who perceived the crystals in vegetable tissue, namely in the rhizome of Iris florentina and in species of Smilax, and this could only be done with strong magnifying powers. In other matters he repeats the histological views of Malpighi and Grew, and on the whole his numerous communications seem painfully fragmentary and unscientific in presence of Malpighi’s elegance and perspicuity, and Grew’s systematic thoroughness. His figures too, which were not drawn by himself, are with some exceptions inferior to those of his great contemporaries.
[CHAPTER II.]
Phytotomy in the Eighteenth Century.
Malpighi had no successor of note in Italy; in England the new light was extinguished with Hooke and Grew, and has so remained, we may almost say, till the present day; in Holland also Leeuwenhoek found none to follow him of equal rank with himself, and the work done in Germany up to the year 1770 is more wretched than can well be imagined. There was in fact no original phytotomic research in the first fifty or sixty years of the last century; the accounts which were given of the structure of plants were taken from Malpighi, Grew, and Leeuwenhoek by persons, who, unable to observe themselves, did not understand their authors and stated things not to be found in their writings. The feebler and obscurer notions of the older writers were preserved with a particular preference, and thus it was Grew’s complicated idea of the web-like structure of cell-walls that made most impression on those who reported him. This state of decline must not be ascribed to imperfect microscopes only; these certainly were not good, and still less conveniently fitted up; but no one saw and described clearly even what can be seen with the naked eye or with very small magnifying power; the worst part of the case was that no one tried fully to understand either the little he saw himself or the observations to be found in older works, but contented himself from want of reflection with most misty notions of the inner structure of plants. It is not easy to discover the causes of this decline in phytotomy in the first half of the 18th century; but one of the most important appears to lie in the circumstance, that botanists, following in this the example of Malpighi and Grew, did not make the knowledge of structure the sole aim in their anatomical investigations, but sought it chiefly for the purpose of explaining physiological processes. The food and circulation of the sap of plants were more and more the prominent questions, and Hales showed how much may be done in this direction even without the microscope; the interest therefore of the few, who like Bonnet and Du Hamel occupied themselves almost entirely with vegetable physiology, was concentrated on experiment.
Others who knew how to use the microscope, as the Baron von Gleichen-Russworm and Koelreuter, were drawn away from the examination of the structure of vegetable organs by their attention to the processes of fertilisation and especially of propagation. The real botanists, according to the ideas of the time, and specially those who belonged to the Linnaean school, considered physiological and anatomical researches generally to be of secondary importance, if not mere trifling, with which an earnest collector had no need to concern himself. That Linnaeus himself thought little of microscopical phytotomy is sufficiently shown by what has been said of him in the first book.
It is not worth while to notice each of the few small treatises on the subject which appeared towards 1760, for they contain nothing new; a few examples will show the truth of the opinion here expressed on the general condition of phytotomy at this time.
We first of all encounter a writer, whom few would expect to find among the phytotomists, the well-known philosopher Christian Baron von Wolff, who in his two works, ‘Vernünftige Gedanken von den Wirkungen der Natur,’ Magdeburg (1723) and ‘Allerhand nützliche Versuche,’ Halle (1721) gives here and there descriptions of microscopes and discusses subjects connected with phytotomy. This he does more particularly in the latter work, where he describes a compound microscope with a focussing lens between the objective and the ocular but without a mirror, an instrument which must have served therefore for observing with the light from above on an opaque surface; the objective was a simple lens. But to magnify objects more strongly, he says that he used a simple instead of this compound instrument, as was more the custom at the time. Like a true amateur Wolff submitted all sorts of small and delicate objects to his glass, without examining any of them thoroughly and persistently. His phytotomic gains were small; he observed for instance that starch-flour (powder) consists of grains, but believed from the way in which they refracted light that they were small vesicles filled with a fluid; yet he satisfied himself that these grains are already in the grains of rye and therefore not produced in the grinding. He laid thin sections of portions of plants on glass which was too imperfectly polished to allow of his seeing anything distinctly. His pupil Thümmig in his ‘Meletemata’ (1736) addressed himself to the subject with still less skill. By the case of these two men we may see plainly that want of success was due much less to the imperfectness of the microscope than to unskilful management and unsuitable preparation. But Wolff and Thümmig at least endeavoured to see something for themselves of the structure of plants; a famous botanist of the time, Ludwig, plainly never made a similar attempt, for in his ‘Institutiones regni vegetabilis’ (1742) he speaks of the inner structure of the plant in the following manner; ‘Laminae or membranous pellicles, so connected together that they form little cavities or small cells and often reticulated by the intervention of fine threads, form the cell-tissue which we see pervading all parts of plants. These are what Malpighi and others call tubes, since they appear in different parts in the form of rows of connected vesicles!’ Boehmer’s ‘Dissertatio de celluloso contextu’ (1785) is still worse; ‘White elastic thicker or thinner fibres and threads woven together of differing shape and size form cavities or cells or caverns, and are usually known by the name of cell-tissue.’ We see what mischief Grew did with his theory of the fibrous structure of the cell-walls, and how the expression cell-tissue literally taken led the botanists here named and others into utterly incorrect ideas. The works of Du Hamel, Comparetti, and Senebier show that such misconceptions were not confined to Germany, and Hill, a countryman of Grew, according to von Mohl’s account pictured to himself cells as cups standing one above another, closed below and open above.
Baron von Gleichen-Russworm (1717-1783), privy counsellor to the Margrave of Anspach, gave much attention to the perfecting of the mechanical arrangements of the microscope, but his plates themselves show how strangely unsuitable these arrangements were. With these instruments he made many observations, which are recorded in two voluminous works, ‘Das Neueste aus dem Reich der Pflanzen’ (1764) and ‘Auserlesene mikroskopische Entdeckungen’ (1777-1781). But these works contain little or nothing about microscopic anatomy or the structure of vegetable cells. His observations with the microscope are chiefly devoted to processes of fertilisation and to proving that spermatozoa are contained in the pollen[69], and in connection with these subjects he gives magnified figures of many small flowers, some of them beautifully executed; these figures must have made his works very instructive to many in their time. He saw the stomata, which Grew had already discovered, on the leaves of ferns, but took them for the male organs of fertilisation, which at the same time showed that he was still unacquainted with the existence of stomata in phanerogams.