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Show 430 DARWINISM CHAP. of natural selection, but must be regarded as naturally traceable to the vegetative checking of their respective types of leaf organ. Again, a detailed examination of spiny phtnts pra-ctically excludes the hypothesis of mammalian selection altogether, and shows spines to arise as an expression of tho diminishing vegetativeness-in fact, the ebbing vitality of a, species.1 Objections to the Theory. The theory here sketched out is enticing, and at first sight seems calculated to throw much light on the history of plant development; but on further consideration, it seems wantin ()' in definiteness, while it is beset with difficulties at every ste1~ Take first the shortening of the raceme into the umbel and the capitulum, said to be caused by arrest of vegetative growth, due to the antagonism of reproduction. If this were the whole explanation of the phenomenon, we should expect the quantity of seed to increase as this vegetative growth diminished, since the seed is the product of the reproductive energy of th~ pla?t, and its quantity tho best measure of that energy. But IS th1s the case 1 The ranunculus has comparatively few seeds, and the flowers are not numerous ; while in the same order the larkspur and the columbine have far more soecls as well as more flowers, but there is no shortening of the raceme or diminution of the foliage, although the flowers are largo ancl complex. So, the extremely shortened and compressed flowerheads of the compositre produce comparatively few seeds -one only to each flower ; while the foxglove, with its long spike of showy flowers, produces an enormous number. Again, if the shortening of the central axis in the successive stages of hypogynous, perigynous, and epigynous flowers wore an i?dication of preponderant reproduction and diminished vegot:t· twn, we should find everywhere some clear indications of this fact. The plants with hypogynous flowers should, as a rule, have less seed and more vigorous and abundant foliage than those at the other extreme with epigynous flowers. But tho 1 This brief inuicatiou of Professor Gedde ·'s views is taken from ihc article "Variation and Selection" in the Encycloprodia B1·itannica, and a paper "On theN ature and Causes of Variation in Plants" in Tmns. and P1·oc. of the Edinburgh Botanical Society, 1886 ; and is, for the most part, expressed in his own words. XIV FUNDAMENTAL PROBLEMS 431 hypogynous poppies, pinks, and St .. John's ":orts have_ abundanee of seed and rather scanty fohago ; while the ep1gynous do<,.woods and honeysuckles have few seeds and abundant foliage. If, instead of the number of the s_eeds, we take the size of the fruit as an indication of reproductiVe energy, we find this at a maximum in the gourd family, yet their rapid and luxuriant growth shows no diminution of vegetative power. So that the statement that plant modifications proceed " along an absolute O'roove of progressive change" is contradicted by 0 . . innumerable facts indicating advance and regression, Improve-ment or degradation, according as the ever-changing environment renders one form more advantageous than the other. As one instance I may mention the Anonacere or custard-apple tribe which are certainly an advance from the Ranunculacere ; yet in the genus Polyalthea tho fruit consists o! a num~er of separate carpels, each borne on a long stalk, as If revertmg to the primitive stalked carpellary loaves. On the Origin of Spines. But perhaps the most extr~ordinary ap:plic~tio_n of the theory is that which considers spmos to be an md1eat10n of the "ebbing vitality of a species," and which excl~des "mammalian selection alto()'ether." If this were true, spmes should occur mainly in feeble, rare, and dying-out species, instead of which we have the hawthorn, one of our most vigorous shrubs or trees, with abundant vitality and an extensive range over the whole Palrearctic region, showing that it is really a d~minant species. In North America the numerous thorny speCies of Cratregus are equally vjgorous, as are the false acacia (Robinia) and the honey-locust (Gleditschia). Neither have the numerous specjes of very spiny Acacias. been noticed to be rarer or less vi()'orous than the unarmed kmds. 0 On tho other point-that spjnes are not due to. mamm~lian selection-we are able to adduce what must be considered direct and conclusive evidence. For if spines, admittedly produced by aborted branches, petjoles, or peduncles, are due solely or mainly to diminished ve()'etativeness or ebbing vitality, they ought to .occur in all countries alike, or at all events in all whose similar conditions tend to check vegetation ; whereas, if they are, .solely or mainly, developed as a protection against the attacks |