432 DAR^VIlSriSM chap. 



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 A"aluable information on this point. 

 He says : " There are no spiny or prickly plants in the in- 

 digenous element of the St. Helena flora. The relatively rich 

 flora of the SandAvich 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 Avhich there are many armed species in other countries, 

 are only represented by unarmed sjDecies. 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 inves- 

 tigated 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 Xew Zealand, 

 but there are the formidably armed species of Avild Spaniard 

 (Aciphylla), one species of Eubus, the pungen1>leaved Epacridese 

 and a few others." 



Mr. J. G. Baker of Kew, who has specially studied the 

 flora of IVIauritius and the adjacent islands, also Amtes 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 Avhole group of islands (IVIauritius, 

 Bourbon, Seychelles, and Eodriguez), there \n\\ 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 C[uite inexplicable 

 on the theory of spines being caused solely by checked vege- 

 tative gTowth, due to Aveakness of constitution or to an arid soil 

 and climate. For the Galapagos and many parts of the Sand- 

 Avich Islands are very arid, as is a considerable part of the 

 North Island of New Zealand. Yet in our OAvn moist climate 



