20 MY LIFE [Chap. 



species of white Leptalis as a disproof of Bates' theory of 

 mimicry, — or that only a few species of butterfly resemble 

 leaves, — or that the habits and instincts that protect one 

 animal are absent in allied species. These are all illustra- 

 tions of the many and varied ways in which nature works to 

 give the exact amount of protection it needs to each species." 



3. Arctic Plants in the Southern Hemisphere, and on 

 Isolated Mountain-tops within the Tropics. — Having paid great 

 attention to the whole question of the distribution of organ- 

 isms, I was obliged to reject Mr. Darwin's explanation of the 

 above phenomena by a cooling of the tropical lowlands of the 

 whole earth during the glacial period to such an extent as to 

 allow large numbers of north-temperate and Arctic plants to 

 spread across the continents to the southern hemisphere, and, 

 as the cold passed away, to ascend to the summits of isolated 

 tropical mountains. The study of the floras of oceanic 

 islands having led me to the conclusion that the greater part 

 of their flora was derived by aerial transmission of seeds, 

 either by birds or by gales and storms, I extended this view 

 to the transmission along mountain ranges, and from 

 mountain-top to mountain-top, as being most accordant with 

 the facts at our disposal. I explained my views at some 

 length in " Island Life," and later, with additional facts, ir 

 " Darwinism." 



The difficulties in the way of Darwin's view are twofold 

 First, that a lowering of temperature of inter-tropical low- 

 lands to the required extent would inevitably have destroyed 

 much of the overwhelming luxuriances and variety of plant, 

 insect, and bird life that characterize those regions. This" 

 has so impressed myself, Bates, and others familiar with the 

 tropics as to render the idea wholly inconceivable ; and the 1 

 only reason why Darwin did not feel this appears to be thai 

 he really knew nothing personally of the tropics beyond a 

 few days at Bahia and Rio, and could have had no conception 

 of its wonderfully rich and highly specialized fauna and flora. 

 In the second place, even if a sufficient lowering of tempera- 

 ture had occurred during the ice-age, it would not account foi 



