Page images
PDF
EPUB

take place where he has no part in modifying the conditions under which animals or plants are to live: for, when under his care, they are necessarily the objects of countless experiments on his part; and, in fact, the very process of cultivation or domestication is itself often a long-continued experiment, carried on by generation after generation of men. And it is (as may be inferred from the quotation from Mr. Murphy, in the earlier part of the present chapter) vastly easier to collect observed facts, or gather new ones for ourselves, from those animals and plants which are the objects of constant care and watchfulness, in the domesticated state, than from wild species which are comparatively unnoticed. But we shall find, on examination, variations in a state of nature also, and that the variation, if generally less rapid in each individual case, has been inconceivably greater in amount in the entire wild fauna 1 and flora 2 of the earth than in the comparatively few species which man has taken under his charge. Wild plants, and those in whose culture little care is taken, sport. Every one knows of four-leaved clovers, and I have even seen a specimen of red clover in which

1 The whole series of animals inhabiting any region. 2 The plants of a region.

one of the three leaflets had grown together by its edges in such a way as to make a little

green trumpet of it. The botanist occasionally finds a sensitive fern(a species very common in New England) in which the grape-like fruiting-leaf, or frond, bas on one side of the midrib its usual form, but on the other side has grown into broad leaflets, with the fruit borne in little dots on the under side of each (as is the case with most ferns). Here, then, is the plainest kind of evidence of the possibility of the little grapelike cluster at some time, how long ago no one can even guess, having originated by a variation from the visual sort of fern leaf, or frond as it is more properly called.

Such variations as this one would rather interest botanists than those not specially concerned with the study of plants, but there are hosts of freaks displayed in the growth of wellknown species. What boy does not know of some hickory (or, as it is called in New England, walnut-tree) which bears nuts of twice the usual size, of a thorn-tree whose fruit is nearly as large as a Siberian crab-apple, and far more palatable, of an oak whose acorns nearly as eatable as chestnuts, or of a thicket

are

1 Oucce: sensibilis, var. cbtusilobata.

of wild plums whose fruit is as much superior to the ordinary wild kind as the Delaware is better than a fox-grape? One who is looking for variations in plants can hardly walk through a bit of woods without finding, here a whole tree, there a branch only, that has rougher or smoother bark, or the leaves more or less cut, more or less hairy, or darker or lighter green, than usual. Every treatise upon botany is full of such variations; and the list of doubtful species — that is, of plants that may be species, or may only be varieties —is so long, that the number assigned for the species in many of the largest genera of flowering plants would, according to some authorities, be half as large again, or even nearly double the number assigned by Bentham and Hooker in their great work on the genera of plants. Alphonse de Candolle, the eminent French botanist, in summing up the result of his observations on the oak genus, says, that, out of the three hundred species which he has enumerated, as many as two hundred are doubtful species; that is, it is impossible to be certain whether they should be counted as species or as varieties.2

1 See an article in The Gardener's Chronicle, June 9, 1883.

2 Darwin's Origin of Species, pp. 40, 41.

Now, this extreme variability, and this linking together of forms which are evidently distinct by others which about equally resemble each of them, is just what we should expect to find if the different species had, as the development theory supposes, descended from some common ancestor.

But this variability is as true of wild animals as it has just been shown to be of wild plants. A few examples only, out of the multitude available, can be quoted here. Among birds, as is well known to students of ornithology, one species is often discriminated from another by the size, in cases where the color and markings of the plumage are found too variable to admit of accurate conclusions being formed from them alone. Yet it has been shown by one of our foremost American ornithologists, Mr. J. A. Allen, that, even in what all agree to call one species, great differences of size occur among full-grown birds, reaching in some cases to from ten to twenty-five per cent of the entire size of the bird ; and these variations are accompanied by no less extensive variations in color and markings. Hawks, sparrows, and flycatchers, among our common birds, afford many examples of variable species which cannot be separated by well-defined lines. Among mammals, too, the same state of things prevails.

1 The Mammals and Winter Birds of Florida, vol. ii. ; No. 3 Bulletin of the Museum of Comparative Zoology at Harvard College.

The lynx, or wildcat genus, is by different authors stated to consist of from one to four species, found in North America and the northern part of the Old World ;1 while certain SouthAmerican genera, the Ocelots and Margays for example, are not less difficult to classify.? So it is, too, with the little insect-eating shrews, the smallest of mammals; while fishes, in many genera, present an even more perplexing problem to the systematic zoologist. Of this the white-fish genus and many genera of minnows are examples; while the North-American garpikes are variously reckoned as consisting of from three to forty species.3

But the most astonishing indefiniteness is found among some of the lowest animals. Dr. Carpenter, one of the foremost zoologists and microscopists in England, has long ago shown that the foraminifera have only “series of forms,” not species. I may explain that the

1 The Cat, St. George Mivart, p. 424. 2 Ibid., pp. 408, 409.

3 Jordan's Manual of the Vertebrates of the Northern United States, p. 341.

4 Quoted by Schimidt, Descent and Darwinism, n 93.

« PreviousContinue »