Page:Darwinism by Alfred Wallace 1889.djvu/456

 of herbivorous mammals, they ought to be most abundant where these are plentiful, and rare or absent where indigenous mammalia are wanting. Oceanic islands, as compared with continents, would thus furnish a crucial test of the two theories; and Mr. Hemsley of Kew, who has specially studied insular floras, has given me some valuable information on this point. 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 genera as Zanthoxylon, Acacia, Xylosoma, Lycium, and Solanum, of which there are many armed species in other countries, 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 includes 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 or spiny.

"Spiny and prickly plants are also rare in New Zealand, but there are the formidably armed species of wild Spaniard (Aciphylla), one species of Rubus, the pungent-leaved Epacrideae 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 (Mauritius, Bourbon, Seychelles, and Rodriguez), there will be about a dozen species, but then nine of these are palms. Leaving out palms, the trees and shrubs of that part of the world are exceptionally non-spinose."

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