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for example, that we go into the fields and gather an armful of plants as they come to hand, and then proceed to sort them, what do we find? It scarcely needs the experiment to assure us that we can throw the contents of our parcel into groups, each of which is composed of a larger or lesser number of individual specimens. But a little close inspection will show that our first sorting has by no means disposed of the business. Some of our groups will give us no difficulty; although the individuals composing it are not as absolutely identical as if they were cast in the same mould, yet they so closely agree that we have no difficulty in associating them. A closer scrutiny of other groups will show that they are by no means so homogeneous. We have probably a group of buttercups, which, when we come to scrutinise it carefully, turns out, notwithstanding their general resemblance, to be composed of at least three distinct sorts. The distinctions are tangible and definite, but require careful scrutiny for their recognition. Our primary group has therefore to be broken up into subordinate ones. When we have carried discrimination till it is exhausted, we may survey the result. We shall be struck by the inequality of the differences which separate our groups. Some will appear to only differ in inconsiderable details; others not to have a single point in common. It is clear, then, that we have groups of two very different kinds.
If—as we may obviously do, without altering the essential nature of the problem—we substitute for the limited area from which we have drawn our material the whole field of Nature, we are face to face with a problem which has occupied science, as far, at any rate, as plants are concerned, since the sixteenth century—the classification of living things.
The study of botany developed out of medicine, and the first attempts of botanical writers were to enumerate and group plants which were useful in pharmacy or the arts. Such attempts, based on their properties, were soon seen to be inadequate. A scrutiny of the plants themselves led to classifications, more or less imperfect, resting on structure. It is interesting to observe that while Chinese botanical literature still remains in the stage corresponding to that of the fifteenth century in Europe, that of Japan, even before it came under European influence, in so far as it accurately discriminated native plants, was two centuries in advance. The explanation is in each case the same: the method in the one case was purely literary, and relied on tradition; in the other it went to Nature for its facts.
It is obvious that classification would soon need a formal terminology. For this it went to logic, with the result that it borrowed trammels which clung to it like a shirt of Nessus down to the time of Darwin. Naturalists adopted for a group of individuals which resembled each other more closely than any other individuals the term species; similarly, for groups of resembling species, the term genus. As Mill remarks, these terms are 'used by naturalists in a technical 'acceptation, not precisely agreeing with their philosophical 'meaning.' And he adds :—
'It should be observed that, in ordinary parlance, not the name of the class, but the class itself, is said to be the genus or species; not, of course, the class in the sense of each individual of that class, but the individuals collectively and considered as an aggregate whole; the name by which the class is designated being then called not the genus or species, but the generic or specific name.' (System of Logic, vol. i. p. 134.)
And this is common sense; unfortunately it took naturalists two hundred years to arrive at it.
Although Kaspar Bauhin (1550-1624), the first great botanical systematist, had practically carried out in his writings the distinction between genus and species, and so anticipated Linnaeus in the principle of binary nomenclature, it was another illustrious son of Cambridge—John Ray (1628-1705)—who formally introduced the terms, which he perhaps adopted, with much else, from a little-known writer, Jung (1587-1657), who was the founder of modern botanical terminology.
With the terms, naturalists derived from logic a good deal that was far less useful. Not satisfied with using the word species as a designation for the totality of individuals differing from all others by marks or characters which experience showed to be reasonably constant and trustworthy, as is the practice of modern naturalists, they required that it should receive a formal definition. Biological science thus hampered itself with scholastic fetters which it has not completely shaken off even at the present day. Ray, who may be taken as practically the father of 'species,' at any rate as far as the vegetable kingdom is concerned, found a criterion in the distincta propagatio ex semine. In other words, he was satisfied if species 'came true from seed.' But this would raise to specific rank every bean or cabbage we cultivate in our gardens, and therefore fails. Another criterion was what has been termed 'the rash generalisation that distinct species are to be recog'nised by their incapacity to produce fertile hybrids.' Darwin dealt with this at great length; but it was reasserted by Wagner, and remained a stumbling-block even with Huxley to the last. It was, however, the doctrine of the 'constancy of species,' and the consequent denial of the existence of variation in Nature, which ultimately proved one of the greatest obstacles to the acceptance of the Darwinian theory. It was really implied by Ray, but expressed in the most extreme form by Linnaeus. 'We reckon so 'many species as there were distinct forms created in prin'cipio.' As a necessary corollary to this, he denied the possibility of the appearance of new species. These, as Lange says, are ' the traditions of Noah's ark.' * All this was mere assertion; but Darwin himself has told us that 'when I was on board the "Beagle" I believed in the per'manence of species.' f
But the dogma assumed its most definite form in a different way. Mill's 'ordinary parlance,' unfortunately, did not govern the use of the terms genus and species. They were not applied to the aggregate of individuals included in them, but to the distinctive marks or characters by which they are defined. Such a definition is an abstraction, but under the influence of the scholasticism with which Linneeus was himself imbued it came to be regarded as having a real existence. And the same principle was applied to the higher groups into which genera were collected. Thus we have the Swedish botanist, Elias Fries, in 1835, maintaining that each division ideam quandam exponit. 'Every natural species,' says Shadworth Hodgson, ' in fact, seemed to owe its exist'ence to an idea or conceived type, existing as an idea or 'conception previously to the existence of the individuals 'of the species which realised it, and determining the indi'viduals to be what they were, in order to realise it.' J We shall see to what monstrous growth this sort of idealism ultimately attained, and how powerful was its influence in retarding the growth of progress in biology. We may well agree with Lange that 'There is in the whole of modern 'science, perhaps, no such instance of so empty and, at the 'same time, so crass a superstition as that of Species, and 'there are probably few points in which men have gone on 'rocking themselves with such baseless argumentations into 'dogmatic slumber.' §
* History of Materialism, vol. iii. p. 27. t Huxley, 'Essays,' vol. ii. p. 275.
i Metaphysic of Experience, vol. ii. p. 275. § L.c, vol. iii. p. 27. VOL. OXCVI. NO. OOCCII. C C
If the scholastic fetters of the constancy of species hindered naturalists from seeing facts as they are, the necessity of doing so was nevertheless thrust on their notice in another way. If species had been created, as Linnaeus assumed they had been, it might be supposed that they would differ pretty uniformly. But it is a matter of common observation that this is not the case: they are separated into groups, and the different kinds of roses, for example, are much more like one another than they are like brambles. As has been seen, the formation of genera for groups of species which had many points in common was accomplished very early. When, however, it was attempted to repeat the grouping process on genera, and collect them into groups of a higher order, great difficulties presented themselves, which, even to the present day, have not been wholly surmounted, and perhaps never will be. But the demand for a classification of some kind has always been an imperious necessity, if only to make the detailed knowledge of natural productions, as it accumulated, available for use. The examination of a ' Post Office 'Directory ' will show that a classification may proceed on widely different principles. It may be either purely arbitrary, or more or less rational. An alphabetical arrangement relies on a circumstance which has no sort of significance, and is an example of the former; an arrangement by streets or occupations proceeds on a definite principle, which, though imperfect, illustrates the latter. In utilising the material for purposes of economic inquiry more instructive methods might be devised.
L'Obel (1538-1616), who spent much of his life in England, and died here, did not occupy himself with genera, but was the first to recognise, as we do still, certain large groups of plants, such as Grasses, Umbellifers, Papilionaceous Plants, and Labiates. He laid down the fundamental principle which systematists strive to this day to follow: 'Ordo utique sibi similis et unus progreditur ducitque a 'sensui propinquioribus et magis familiaribus ad ignotiora 'et compositiora.' Kaspar Bauhin, the real founder of systematic botany, followed on the same track. Our own countryman Ray was a century in advance of his time in his attempts at a real classification, and he laid down the true principle: 'Methodum intelligo naturae convenientem 'quae nee alienas species conjungit nee cognatas separat.' Linnaeus was deterred from the task by the pressing necessity of introducing some merely practical method into the chaos into which nomenclature had fallen. He, therefore, invented what was avowedly an artificial system, which had the immense practical merit of enabling those who used it to name their plants with little difficulty. But he never lost sight of the unsolved problem of the construction of a natural system, which should exhibit the true relationships of the members of the vegetable kingdom. The intellectual indolence of mankind is incorrigible. The Linnean system, which its founder avowedly proposed as a mere provisional expedient, came to be regarded in Germany and England as final. But France, whose quicker imagination has often saved the situation in science, was never enthralled by Linnaeus, and the developement of a natural system was in the main finally achieved by the labours of Jussieu.
That Linnaeus, great as his powers were of co-ordinating facts, was deterred from the task is not surprising. For, though the homogeneousness of such groups as L'Obel marked out almost 'jumps to the eyes,' the discovery of true relationships becomes more and more difficult as we proceed. One cause of this was first clearly pointed out by Auguste de Candolle. The true marks in any living organism which indicate relationship are often overlaid by superficial characters which only have relation to the, so to speak, accidental mode of life of the individual species: such characters we now call 'adaptive.' De Candolle distinguished the former as morphological, and the others as physiological. An illustration will suffice. One of the largest and most widely distributed genera in the vegetable kingdom is that of Senecio, of which the common weed, groundsel, is a representative in this country. Yet another species of Senecio has been mistaken for ivy: some are succulent, like cacti; others are shrubs or trees. They masquerade in every possible guise; but the perplexed novice may console himself with the knowledge that they have entrapped even the most astute botanists. Yet they are betrayed by easily detected, though less obvious, characters, notwithstanding the bravery with which they sometimes flaunt, and are inevitably brought down to the level of the humble groundsel.
But we owe to Robert Brown, the greatest botanist whom Britain ever produced, the last clue to the mysteries of a natural system—the study of developement. In some cases everything that meets the eye will only put one on the wrong track: it is only, as it were, in 'becoming' that the structure of species reveals their true relationships.
The historical developement of the natural system has