XII GEOGRAPHICAL DISTRIBUTION OF ORGANISMS 369 



violent and long-continued gales of wind, we shall not only be 

 better able to account for the floras of some of the remotest 

 oceanic islands, but shall also find in the fact a sufficient ex- 

 planation of the wide diffusion of many genera, and even species, 

 of arctic and north temperate plants in the southern hemisphere 

 or on the summits of tropical mountains. Nearly fifty of the 

 flowering plants of Tierra-del-Fuego are found also in North 

 America or Europe, but in no intermediate country ; while fifty- 

 eight species are common to New Zealand and Northern Europe; 

 thirty-eight to Australia, Northern Europe, and Asia ; and no 

 less than seventy-seven common to New Zealand, Australia, 

 and South America. i On lofty mountains far removed from each 

 other, identical or closely allied plants often occur. Thus the 

 fine Primula imperialis of a single mountain peak in Java has 

 been found (or a closely allied species) in the Himalayas ; 

 and man}^ other plants of the high mountains of Java, Ceylon, 

 and North India are either identical or closely allied forms. So, 

 in Africa, some species, found on the summits of the Cameroons 

 and Fernando Po in West Africa, are closely allied to species 

 in the Abyssinian highlands and in Temperate Europe ; while 

 other Abyssinian and Cameroons species have recently been 

 found on the mountains of Madagascar. Some peculiar Aus- 

 tralian forms have been found represented on the summit of 

 Kini Balu in Borneo. Again, on the summit of the Organ 

 mountains in Brazil there are species allied to those of the 

 Andes, but not found in the intervening lowlands. 



No Proof of Recent Lower Temperature in the Tropics. 



Now all these facts, and numerous others of like character, 

 were supposed by Mr. DarAvin to be due to a lowering of 

 temperature during glacial epochs, which allowed these tem- 

 perate forms to migrate across the interA^ening tropical low- 

 lands. But any such change within the epoch of existing species 

 is almost inconceivable. In the first place, it would necessitate 

 the extinction of much of the tropical flora (and with it of the 

 insect life), because ^nthout such extinction alpine herbaceous 

 plants could certainly never spread over tropical forest low- 



^ For fuller particulars, see Sir J. Hooker's Introduction to F/or>s of Xew 

 Zealand and Australia, and a summary iu my Island Life, chaps, xxii. 

 xxiii. 



2b 



