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Show 43~ DARWINISM CllAJ'. of herbivorous mammals, they ought to be most abundant where these are plentiful, a.nd rare or absent where indigenous mammalia are wanting. Oceanic island , as compared with continents, would thus furnish a crucial test of the two theories; and Mr. Hemsley of Kew, who has specially studied in ula1· floras, has given me some valuable information on this poiut. He says : " There are no spiny or prickly plants in the indigenous element of the St. Helena flora. The relatively rich flora of the Sandwich Isles is not absolutely without a prickly plant, but almost so. All the endemic genera are unarmed, and the endemic species of almost every other genus. Even such genem as Zanthoxylon, Acacia, Xylosoma, Lycium, and Solanum, of which there are many armed species in other countric. ·, are only represented by unarmed species. The two endemic Rubi have the prickles reduced to the setaceous condition, and the two palms are unarmed. "The flora of the Galapagos inclu les a number of prickly plants, among them several cacti (these have not been investigated and may be American species), but I do not think one of the known endemic species of any family is prickly m· spiny. "Spiny and prickly plants are also rare in New Zealand, but there arc the formidably armed species of wild Spaniard (Aciphylla), one species of Rubus, the pungent-leaved Epacri<.lere and a few others." Mr. J. G. Baker of Kew, who has specially studied the flora of Mauritius and the adjacent islands, also writes me on this point. He says : "Taking Mauritius alone, I do not call to mind a single species that is a spinose endemic tree or shrub. If you take the whole group of islands (Mauritiw:;, Bourbon, Seychelles, and Rodriguez), there will be about n. dozen species, but then nine of these are palms. Leavi11g out palms, the trees and shrubs of that part of the world. nrc exceptionally non-s]Jinose." These are certainly remarkable facts, and quite inexplicable on the theory of spines being caused solely by checked vegetative growth, due to weakness of constitution or to an arid soil and climate. For the Galapagos and many parts of the Sandwich Islands are very arid, as is a considerable part of the North Island of New Zealand. Yet in our own moist climate XIV FUNDAMENTAL PROBLEMS 433 and with onr very limited number of trees and shrubs we ha.vc n.bout eighteen spiny or prickly species, m?1~c, apfarent.ly, than in the whole endemic floras of the Mauntms, Sand w1ch Isla.nds, n.nd Galapagos, though these arc all especially. rich in ·hrubby and arboreal species. In New Zealand the pnckly Rubus is a leafless trailing 1 lant, and its prickles a.rc probably a. protection against the larrre snails of the countt:y, scvera.l o~ which have shells from two to three :111<l :1 ha.lf mchcs long. The "wild Spaniards" a.rc very spiny herbaceous Umbellifc:re, and may ha.ve gained their spines to preserve them from bcmg trodden down or eaten by the Moas, which, for countless a.ges, took the place of mammals in N cw Zcabnd. The exact usc or meaninrr of the spines in palms is more doubtful, though they arc, ;o doubt, protective against some animals ; but it is certainly an extraordinary fact that in the entire flora of the Mauritius, so largely consistincr of trees and shrubs, not a sinctlc endemic species should. be thorny or spiny. If now we consider that every continental flora produces a considerable proportion of spiny and t~orny spccicR, u ~d that these rise to a maximum in South Afnca, where hcrb1 vorous mammalia were (before tho settlement of the country), perhaps, more abundant and varied than in any other part of the world· while another district, remarkable for well-armed vcget~tion, is Chilo, where the camel-like vicugnas, llamas, and alpa.cas, and an abundance of large rodents wage perl?et~al war against shrubby vegetation, we shall sec th~ full sigm~cance of the almost total absence of thorny and spmy plants m the chief oceanic islands; and so far from "excluding the hypothesis of mammalian sclccti~n altogether," we. shall find in this hypothesis the only satisfactory explanatiOn of the facts. From the brief consideration of Professor Geddes's theory now gi von, we conclude that, although the antagoni m between vecrctative and reproductive growth is a real agency, and must be 0taken account of in our endeavour to explain many of the fundamental facts in the structure and form of plants, yet it is so overpowered and directed at every . top by the natm:al selection of favourttble variations, that the results of 1ts 1 Placostylis bovinus, 3~ inches long; Parypbanta Busbyi, 3 in. diam. ; P. Hochstetteri, 2!! in. diam. 2 F |
