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XXI.-SPECIES AND SUBSPECIES.
DES MATERIAUX À UNE FLORE REFORMÉE DE LA FRANCE, ET
TWENTY, or even ten years ago, the publication of a work such as that which we now propose briefly to notice, would have attracted little attention in the botanical world. By all botanists engaged on a general survey of the vegetable kingdom, and therefore accustomed to broad views of the nature of species, it would have been regarded as a mere puzzle. They would have felt that they had little or nothing in common with an author whose opinions were so different from their own. The school of local botanists, as it has been called, of men who devoted themselves to the minute observation of a limited number of plants, inhabiting a confined area, was becoming more and more separate from that of general botanists. The views of the two schools on the nature and limitation of species, were indeed utterly at variance, with little or no prospect of their being reconciled. The general botanist, trying to grasp the whole range of plant forms, and thus accustomed to deal with large numbers, came to overlook or under-estimate the importance of minute characters. From the very nature of his studies he had a bias in favour of combination, rather than separation. The local botanist had a smaller number of objects of study. He, therefore, looked at them more closely, and became familiar with points of difference which escaped the other, but, at the same time, lost sight of the points of resemblance, which at once caught the attention of the general observer. Each of these two classes of naturalists was right from his point of view, but each had something to learn from the other.
Fortunately for the progress of science, the current of thought on the question of species, has, within the last few years, received an entirely new direction, and acquired new vitality, by the publication of the admirable speculations of Darwin and Wallace. Whether we adopt or reject the Darwinian hypothesis, we must equally appreciate the great mass of new and unexpected facts, which its originators and supporters have brought forward in its favour. It would be premature to say that it has put an end to the differences between the two classes of observers, but there can be
little doubt that it has bridged over the chasm which separated them, and that by enabling both to look at the question from a new point of view it will, in the end, lead to agreement.
Darwin's marvellous observations have of late set all the world thinking about variation and variability, and have already stimulated to an enormous extent the observing faculties of naturalists. It is, therefore, a matter of interest, at the present time, to know what a zealous advocate of the immutability of species, and the champion of the school of minute observers, has to say for himself. M. Jordan's views, on both these subjects, are well known to be extreme. He not only believes in the permanence of species throughout all time, but looks upon this rather as a postulate to be taken for granted, than as a matter to be proved. Those who differ from him on this point are too heterodox to be reasoned with. Strange pantheistic phantoms flit before his eyes when he thinks of their plausible but dangerous heresies. With such fears and fancies we need not meddle. Fortunately, when we abstract them, we find him, in many respects, an acute, patient, and careful observer, and withal, as we believe, perfectly conscientious. A firm believer in his own results, and isolated in a great measure by their peculiar nature, he is sadly disappointed that they are not universally adopted, regards himself as a martyr to science, looks forward to the appreciation of posterity as a recompense for the neglect with which he is treated by the present generation of naturalists ; compares himself, of course, to Galileo, and applies very hard names to all who refuse to accept his conclusions. It is no doubt a pity that he cannot bring himself to gire to others the same credit for good faith which he so emphatically claims for himself, and that he should go out of his way to impute improper or unworthy motives to those who differ from him in the inferences to be drawn from observed facts. Unappreciated discoverers are however, as a rule, susceptible, and we must be content to take the abuse, and, at the same time, to glean what we can from a work which contains, along with much that is improbable and unsatisfactory, a great number of curious observations, and from the very faults and mistakes of which we may learn a valuable lesson.
M. Jordan has been in the habit for many years of cultivating in his garden a great variety of plants, introduced from various parts of France, or raised from seeds collected by himself, or sent to him by his correspondents. Annual plants he often sows broadcast
in the fields or pastures near his house, where many become perfectly naturalised, and reproduce themselves year after year. He has thus (he thinks) excellent opportunities of observing the permanence or variability of forms. He tells us that these experiments and observations have been carried on for twenty-five years. In one case he takes us back to the year 1829, often for ten, twelve, or fifteen years, but in some cases only for three, four, or five years. He was led to this course of study by observing that, in a state of nature, plants, comprehended under the same name, presented differences which, though not very conspicuous, seemed to him certainly not merely individual. On inquiry, he found that the leading botanists of the day explained these differences by variability of type, an explanation which did not satisfy him, and which, therefore, made him wish to observe for himself the existence of the variability thus taken for granted. He therefore repeated his observations on more numerous individuals in their native places of growth, selecting them in all states and of all ages. As he still got the same result, he proceeded to cultivate the several forms in his garden, or in some other easily accessible place. Finding that they always remained constant year after year, it became evident to him that they were more than casual forms. He then raised each separate form repeatedly from seed, and as they still retained all the characters of the parent plant, any remaining doubt was changed to certainty. It became evident that each form was a distinct species, and it was then a matter of necessity to give it a name, so that it might be known from other species, from which nature itself had distinguished it.
In the broadest and most positive terms M. Jordan gives it as the result of his experience, not only that wild plants when transplanted into his garden retain their characters unaltered throughout a long succession of years, but that their seeds produce year after year, invariably, the same form as the parent plant. Once only, so far as we have observed, does he give a hint of slight variation in the offspring. In describing the species (ten in number) allied to Erysimum Bocconei, he tells us that they are all so closely related to each other that, without good specimens and great attention, they cannot be distinguished in the Herbarium. At first therefore, he says, one would be inclined to regard them as modifications of one common type ; but this, though specious, would be wrong, as he has raised them many times from seed since 1840 and 1841, in which years he collected the greater number of them. Slight variations were sometimes observed in the size of the flowers and leaves, and in the length of the pod and style, dependent on the season and on the condition of the plants, but their distinctive characters have, on the whole, remained constant, and at the time he wrote, young plants of each of the ten species were growing in his garden, and were all readily recognized by the leaves alone. Even such trifling deviations as these, from a fixed type, are, however, it is evident, rare in his experience.
In the case of annual plants, M. Jordan has, during a long series of years, seen closely allied forms of Papaver, Erophila, Viola, Geranium, Erodium, &c., growing intermixed with each other in a wild or naturalised state in his own neighbourhood, and invariably coming up true from seed by hundreds and thousands, or sometimes, tens of thousands. Each form, during the whole time, has retained its special distinctive character, though all were under exactly the same external conditions. These forms, however closely allied, are therefore to him true unities, perfectly limited and distinct, constant and invariable in their differences, and completely irreducible one to the other. In a word, they have all the characters of true species, in the ordinary meaning of that word. To call them varieties would, in his opinion, imply that they are now different from what they were created, a gratuitous and improbable hypothesis as much opposed to facts as to reason. Even when the differences, though quite definite, are too minute to attract the attention of ordinary unskilled observers, or to be detected at the first glance, they are, for our author, not the less of specific value.
It is well to observe that by the phrase unskilled observers, we are not to understand one who is entirely ignorant of natural science. The term is meant to include every botanist, however learned and experienced, who is without the special training necessary for the appreciation of minute differences. We need scarcely say that no one but M. Jordan will accept an induction based upon observations continued during 25 years (or a less number), as an infallible proof of invariability. It is evident that M. Jordan has approached the investigation of the question, with preconceived ideas of the duration of the world and of the original mode of the creation of species, which have given a bias to bis modes of observation, and unconsciously led him into error. With the light which other observers have, of late years, thrown upon the subject, it is more important to notice that there is not in any part of the book before us the slightest mention of cross-impregnation, or of insect action in plant fertilization. It would appear that the possibility of either has never for a moment been present to his mind. With the recognition of the powerful influence of insect agency, the whole edifice, raised with so much pains, tumbles to the ground. The facts may stand, but they acquire a different meaning, and lead to quite different conclusions. Every one knows how little reliance can be placed on the results of experiments, in the course of which a great number of closely allied forms are grown together. We are all familiar with the effects of the “visits of bees," and know how difficult it is, even with a net, " to keep out small diptera.”
The conclusions drawn from observations on seedling plants grown promiscuously must therefore be set aside altogether, as at the best unsatisfactory and unconvincing. We are quite willing to believe, on M. Jordan's authority, that the different closely allied forms re-appeared year after year. How and why this was so is a curious matter for enquiry, but there is nothing at all to show that it was because each form was fertilised by the pollen of the same kind and no other. When a peculiar variety is cultivated alone, with no nearly allied race or species near it, general experience confirms the result obtained by Jordan, of the retention of the characters during a certain number of generations, as many as twenty-five in the experiments before us, a number considerably less than infinite. The third result, the permanency during a short series of years of forms removed from their native place to a garden is also conformable to observation. We are aware that it was at one time thought that such variations were accidental and not hereditary, and that change of locality by removing the cause would effect a return to the normal state of the species. The permanence of slight variations under cultivation has therefore been often appealed to as a proof of specific difference. No doubt any modification of character produced by external causes would disappear with the removal of the cause, just as the changes produced by excess of nutriment, affecting only the luxuriance of the plant, continue only as long as the rich food is supplied. Even these slight varieties are, however, now commonly believed to have a tendency to become hereditary, without being therefore necessarily of specific value.
On the whole, a careful study of M. Jordan's work leads us to conclude that its greatest fault is a want of precise details of the experi