XV A CRITIC OF NATURAL SELECTION ANSWERED 309 



and prickles of so many plants inhabiting dry countries 

 to the direct influence of the conditions under which they 

 live. This, he thinks, is proved by some of these plants 

 losing their spines when grown under other conditions ; 

 he adduces numerous examples of the abundance of spiny 

 plants in such countries as Nubia, Abyssinia, and the 

 Kalahari Desert ; and he again and again reiterates the 

 statement that these characters are "simply the inevit- 

 able results of the action of environment." 



Now if these statements comprised all the facts, that is, 

 if in all dry countries spiny plants abounded, while in all 

 moist or fertile districts they were absent or very rare, the 

 explanation given of their origin would have some plausi- 

 bility. But there is no such general coincidence of aridity 

 of soil or atmosphere with abundance of spiny plants, as 

 very little inquiry will show. Mr. Henslow points out 

 several other plant-characteristics which indicate, and, as 

 he thinks, are directly caused by, aridity. Such are very 

 small, coriaceous, or rolled up leaves, or their complete 

 absence ; a hairy or woolly covering to the whole plant ; 

 succulent foliage ; special protection of the buds ; enor- 

 mous development of roots ; abundance of bulbs and 

 tubers ; together with thickness of bark and various pro- 

 tective coatings to stems and leaves. Now many of these 

 peculiarities are present in the flora of the Brazilian 

 Campos — as well described in the memoir of Eug. 

 Warming on Lagoa Santa — which is referred to by Mr. 

 Henslow as corresponding in many respects with that of 

 other arid regions. Yet the author of this memoir ex- 

 pressly states that " spiny plants are very rare " (p. 463). 

 Again, the plants of the Galapagos present similar indica- 

 tions of aridity — shrubs with minute and almost invisible 

 leaves, for example — yet, except the cacti, which may be of 

 American origin, none of the endemic species are spiny. So, 

 also, the rich Sandwich Island flora contains hardly a single 

 endemic spiny plant ; and I am informed b}^ the Rev. 

 R. P. Murray, who is well acquainted with the botany of 

 the Canaries, that spiny plants are exceedingly rare in 

 those islands, though much of the surface, owing to the 

 porous volcanic rock and the long periods of drought. 



