History of Botany (1530-1860)

by Julius Sachs

The establishment of natural affinities combined with the assumption of the constancy of species, the growth of comparative morphology without the history of development, lastly, the very subordinate attention still paid to the Cryptogams,—these are the special characteristics of the period which has now to be described at greater length.

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Here we must once more call attention to the fact, that Linnaeus was the first to perceive that a system which was to be the expression of natural affinities could not be attained in the way pursued by Cesalpino and his immediate successors. All who have attentively studied the writings of Linnaeus which appeared after the ‘Classes Plantarum’ (1738) must have seen the difference between that way and the one recommended by him—a difference which is the more obvious because Linnaeus himself, like his predecessors, constructed an artificial system on predetermined principles of classification, and always employed it for practical purposes, while he published at the same time in the above-named work his fragment of a natural system, and in the preface set forth the peculiar features of the natural and artificial systems in striking contrast with one another. The first thing and the last, he says in his prefatory remarks to his fragment, which is demanded in systematic botany, is the natural method, which slighted by less learned botanists has always been highly regarded by the more sagacious, and has not yet been discovered. If, he continues, we collect the natural orders from all existing systems (up to 1738), we shall get but a small list of really allied plants, though so many systems have claimed to be natural. He had himself long laboured to discover the natural method and had found out some things that were new; but though he had not succeeded in carrying it through to a perfect work, he would continue his efforts as long as his life lasted. He makes the very important remark, that a key, that is, a priori principles of classification, cannot be given for the natural method, till all plants have been reduced to orders; that for this no a priori rule is of value, neither this nor that part of the fructification, but the simple symmetry alone (simplex symmetria) of all the parts, which is often indicated by special marks. He suggests to those who are bent on trying to find a key to the natural system, that nothing has more general value than relative position, especially in the seed, and in the seed especially the ‘punctum vegetans,’—a distinct reference to Cesalpino. He says that he establishes no classes himself, but only orders; if these are once obtained, it will be easy to discover the classes. The essence of the natural system could not have been more clearly expounded in Linnaeus’ time, than it is in these sentences. He established as early as 1738 sixty-five natural orders, which he at first simply numbered; but in the first edition of the ‘Philosophia Botanica’ in 1751, where the list is increased to sixty-seven, he gave a special name to each group; and he showed his judgment by either taking his names from really characteristic marks, or what was still better, by selecting a genus and so modifying its name as to make it serve as a general term for a whole group. Many of these designations are still in use, though the extent and content of the groups have been greatly changed. This mode of naming is an important point, because it expresses the idea, that the different genera of such a group are to some extent regarded as forms derived from the one selected to supply the name. Many of Linnaeus’ orders do in fact indicate cycles of natural affinity, though single genera are not unfrequently found to occupy a false position; at all events, Linnaeus’ fragment is much the most natural system proposed up to 1738, or even to 1751. It is distinguished from Kaspar Bauhin’s enumeration in this, that its groups do not run into one another, but are defined by strict boundaries and fixed by names.

The Linnaean list is distinctly marked by the endeavour to make first the Monocotyledons, then the Dicotyledons, and finally the Cryptogams follow one another; that the old division into trees and herbs already rejected by Jung and Bachmann, but still maintained by Tournefort and Ray, disappears in Linnaeus’ natural system will be taken for granted after what has been already said of it, and from this time forward this ancient mistake is banished for ever.

In Bernard de Jussieu’s[34] arrangement of 1759 we find some improvements in the naming, the grouping, and the succession, but at the same time some striking offences against natural affinity. He published no theoretical remarks on the system, but gave expression to his views on relations of affinity in the vegetable kingdom in laying out the plants in the royal garden of Trianon, and in the garden-catalogue. His nephew published his uncle’s enumeration in the year 1789 in his ‘Genera Plantarum,’ affixing the date of 1759 given above. The difference between it and the Linnaean fragment does not seem sufficiently marked to make it necessary to reproduce it here. It should be noticed however that Jussieu begins with the Cryptogams, passes through the Monocotyledons to the Dicotyledons, and ends with the Conifers. Adanson’s claims of priority over Bernard de Jussieu (see the ‘Histoire de la Botanique’ de Michel Adanson, Paris, 1864, p. 36) may be passed over as unimportant. The natural system was not advanced by Adanson to any noticeable extent; how little he saw into its real nature and into the true method of research in this department of botany is sufficiently shown by the fact, that he framed no less than sixty-five different artificial systems founded on single marks, supposing that natural affinities would come out of themselves as an ultimate product,—an effort all the more superfluous, because a consideration of the systems proposed since Cesalpino’s time would have been enough to show the uselessness of such a proceeding.

The first great advance in the natural system is due to Antoine Laurent de Jussieu[35] (1748-1836). After all that has been said no further proof is needed that he was no more the discoverer or founder of the natural system than his uncle before him. His real merit consists in this, that he was the first who assigned characters to the smaller groups, which we should now call families, but which he called orders. It is not uninteresting to note here how Bauhin first provided the species with characters, and named the genera but did not characterise them, how Tournefort next defined the limits of the genera, how Linnaeus grouped the genera together, and simply named these groups without assigning to them characteristic marks, and how finally Antoine Laurent de Jussieu supplied characters to the families which were now fairly recognised. Thus botanists learnt by degrees to abstract the common marks from like forms; the groups thus constituted were being constantly enlarged, and an inductive process was thus completed which proceeded from the individual to the more general.

It might appear that the merit of Antoine de Jussieu is rated too low, when we praise him chiefly and simply for providing the families with characters; but this praise will not seem small to those who know the difficulty of such a task; very careful and long-continued researches were necessary to discover what marks are the common property of a natural group. Jussieu’s numerous monographs show with what earnestness he addressed himself to the task; and it must be added, that he was not content simply to adopt the families established by Linnaeus and by his uncle and the limits which they had assigned to them, but that he corrected their boundaries and in so doing established many new families, and was the first who attempted to distribute these into larger groups, which he named classes. But in this he was not successful. His attempt to exhibit the whole vegetable kingdom in all its main divisions, to unite the classes themselves into higher groups, was also unsuccessful, for these larger divisions remained evidently artificial. The three largest groups on the contrary, into which he first divides the world of plants, the Acotyledons, Monocotyledons, and Dicotyledons are natural; but they had been already partly marked out by Ray, afterwards by Linnaeus, and finally in Bernard de Jussieu’s enumerations. Still it is the younger Jussieu’s great and abiding merit, to have first attempted to substitute a real division of the whole vegetable kingdom into larger and gradually subordinate groups for mere enumerations of smaller co-ordinated groups,—an undertaking which Linnaeus expressly declared to be beyond his powers. If then Jussieu’s system was far from giving a satisfactory insight into the affinities of the great divisions of the vegetable kingdom, yet it opened out many important points of view, from which they could afterwards be discovered, and it certainly became the foundation for all further advance in the natural method of classification; for this reason it is necessary to give a view of it in the following table:—

A. L. de Jussieu’s System of 1789.

CLASS.
Acotyledones		I.
Monocotyledones
		Stamina
				hypogyna	II.
				perigyna	III.
				epigyna	IV.
Dicotyledones.
	Apetalae	Stamina
				hypogyna	V.
				perigyna	VI.
				epigyna	VII.
	Monopetalae	Corolla
				hypogyna	VIII.
				perigyna	IX.
				epigyna
					antheris
						connatis	X.
						distinctis	XI.
	Polypetalae	Stamina
				epigyna	XII.
				hypogyna	XIII.
				perigyna	XIV.
	Diclines irregulares		XV.

This table shows that Jussieu did not oppose the Cryptogams, which he calls Acotyledones, to the whole body of Phanerogams, as Ray did under the name of Imperfectae; he rather regards the Acotyledones as a class co-ordinate with the Monocotyledones and Dicotyledones; but this mistake or similar mistaken views run through all systematic botany up to 1840; the morphology founded by Nägeli and by Hofmeister’s embryological investigations first showed that the Cryptogams separate into several divisions, which co-ordinate with the Monocotyledons and Dicotyledons. At the same time the use of the word Acotyledones for Linnaeus’ Cryptogams shows that Jussieu overrated the systematic value of the cotyledons, because, as is seen from the introduction to his ‘Genera Plantarum,’ he was quite in the dark on the subject of the great difference between the spores of Cryptogamic plants and the seeds of Phanerogams. His conception of the organs of generation was essentially that of Linnaeus; hence he judged of the Cryptogams according to the scheme of the Phanerogams, and, not perceiving their peculiarities, he virtually characterised them by negative marks.