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of natural selection may be understood to have turned to account any great or small variations in a desirable direction, and preserved them, till the present wonderful series of adaptations is the consequence. That this has been the method by which the existing adaptations have been reached seems all the more likely from the fact, that, in nearly all the classes of phenomena described in this chapter, there are arrangements to be met with, of all degrees of perfection, for securing the desirable result.
If every protective coloration or resemblance were as perfect as that of the arctic hare, or of the leaf-insect of Java, or if every warningcolor were as brilliant as that of the Central American tree-frogs, or if all the provisions made for the distribution of seeds were effective as we find in the case of some burs, or if every case of insect-fertilization secured the necessary result as perfectly as is done in the salvia, it might well be asked, “Where are the successive steps by which this perfect adaptation of means to ends must (according to the development theory) have been reached?” But it is, in fact, far oftener the case, that the adaptation is very imperfect, than that it is as faultless as in the examples just referred to. In the katydid and the common green grasshopper the
same kind of modifications as those which may be supposed to have given rise to the leaf-insect. have proceeded but a little way. The snowbunting is only partially white, and therefore not protected to any such degree as the ptarmigan. It would seem that the banded body of the hornet, and the steel-blue, metallic-looking body of the mud-wasp, must be useful to them mainly or altogether as warning-colors, which would protect them from the attacks of other animals, particularly of birds, many of which are known not to eat stinging insects. But, from the rapid flight of the insects in question, the protection cannot be nearly as complete for them as it is for the slow-flying heliconias among butterflies, or the tree-frogs, which are in the habit of remaining for hours nearly motionless.
Of the seeds which are known to be in some way especially adapted for dispersal, only a few are so perfectly provided for as the cockle-bur or the thistle; but there are far more, which, like the beggar's-ticks or the maple, are provided only with the ineans for securing a short journey. And out of about a hundred thousand known species of flowering plants, there are comparatively few which show adaptations for insect-fertilization at all equal to that of the salvia. In the great majority of cases, even
among those plants which depend on attracting insects, and utilizing their visits, the pollen is jostled off by the insect in one flower, much of it blows away, and only a small portion lodges on his back or head, while of that which does so lodge only an insignificant part is caught upon the stigma of the flower to which le goes.
An alternative explanation to that by means of natural selection, as above outlined, is the hypothesis very recently advanced by Prof. George Henslow, in his “ Origin of Floral Structures.” Professor Henslow attributes the adaptations of flowers to insect-visitors to modifications brought about by the action of the insects themselves, in stimulating and directing the growth of the flowers which they frequent. The more or less rigid tube, in monopetalous 1 or monosepalous ? flowers would, according to this view, have originated as a direct response on the part of the plant to the demand for greater stiffness in the floral envelopes, set up whenever a heavy insect alighted on the flower. Each insect-visit might be supposed to produce an immeasurably small increase in the perfection of the tube as a supporting column, until the adaptation had proceeded as far as, in any given case, it was possible for it to go. In a similar way, the supporting platform formed by the lower lip of the corolla of so many bilabiate 1 flowers inight be explained as produced directly by the pressure due to the weight of insect-visitors and to their efforts to crowd their heads into the interior of the flower. Nectaries 2 may be attributed to the bites of insects seeking for sap or juices with which to moisten gathered pollen, and so on.
1 Flowers with the petals all united together. 2 Flowers with united sepals.
It is as yet too early to pronounce on the relative importance of direct response to external stimuli and of natural selection as factors in the evolution of floral structures. Meantime, it is at any rate clear that Professor Henslow's contribution to the literature of the subject contains the most novel suggestion in regard to the relations of plants and insects that has been advanced for many years.
It is, of course, possible to advance the supposition that all the cases of mimicry and its related phenomena among animals, and of special arrangements for insect-fertilization, and so on, among plants, were created, in all their complexity, just as we now find them. But how would the advocate of such a theory explain the wastefulness and imperfection of the transference of pollen in all but a few exceptional cases, or reconcile such short-comings in the work of an all-wise and all-powerful Creator ? Why, if the vegetable and the animal kingdom were created as we now see thiem, might not every plant have been made capable (as many actually are) of self-fertilization? Or why not have protected the acacias by leaving the leafcutting ants ucreated ? for the latter serve no discoverable useful purpose, but spend their lives in stripping plants of their leaves, and preparing from the bits of leaf artificial musliroombeds or rather mould-gardens, on the product of which they live.
1 Two-lipped flowers, like those of the snap-dragon, etc.
2 The little reservoirs, usually inside the flower and near its base, in which nectar (commonly miscalled honey) is produced.
It is the privilege of the student of natural science to ask such questions as these, and to draw the material for his answers from the heaped-up observations of naturalists everywhere.
And if, from the point of view of the development theory, the phenomena of the living world offer to the observer an exquisite picture of the interaction of natural forces on the living