20 MY LIFE 



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, in " Darwinism." 



The difficulties in the way of Darwin's view are two-fold. 

 First, that a lowering temperature of inter-tropical lowlands 

 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 only reason 

 why Darwin did not feel this appears to be that 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 temperature had occurred 

 during the ice-age, it would not account for the facts, which 

 involve, as Sir Joseph Hooker remarks, " a continuous current 

 of vegetation from north to south," going much further back 

 than the glacial period, because it has led to the transmission 

 not of existing species only, but of distinct representative 

 species, and even distinct genera, showing that the process 

 must have been going on long before the cold period. The 

 reason why Darwin was unaffected by these various difficulties 

 may perhaps be found in the circumstance that he had held his 

 views for so many years almost unchallenged. In a letter to 

 Sir Charles Lyell, in 1866, he says, " I feel a strong conviction 

 that soon everyone will believe that the whole world was cooler 

 during the glacial period. Remember Hooker's wonderful 

 case recently discovered of the identity of so many temperate 

 plants on the summit of Fernando Po, and on the mountains 



