1915-16.] BOTANICAL SOCIETY OF EDINBURGH 15 



(and perhaps others, e.g. Rhododendron) receive as it were 

 a special impetus in Western China and appear there in its 

 greatest variety, though showing at the same time in many 

 cases a close relationship with the species of the next most 

 prolific area, namely the Himalayas ? This is of course a 

 special case of the general problem to which attention is 

 drawn above. 



Finally we may ask. How is it that though China has a 

 flora peculiar to itself characterised by a number of endemic 

 species, and India has quite a different flora characterised 

 by other endemic species, the whole mountainous countr\- 

 from the Himalayas to China shows an unmistakable unit}' 

 in its flora, and a dissimilarity to the floras of the sur- 

 rounding regions in the midst of which it lies, though, as 

 we have seen, the mountain area is not really continuous so 

 far as the emigration of plants is concerned ? It might 

 appear, from a glance at the map, as though the Andes and 

 the Rocky Mountains should show relationship in their 

 floras, and, the reverse being the case, we suspect that the 

 isthmus joining the Northern and Southern Continents was 

 recently under water, a suspicion confirmed by geologists. 

 Similarly while the Rockies support a flora intimately 

 related to that of the Continent, the Andine flora has 

 nothing to do with that of South America, being more 

 closely associated with the New Zealand alpine flora, from 

 which it is inferred that the Andes have been peopled from 

 outside after the distribution of the continental flora, and 

 are therefore a comparatively recent uplift. 



The same argument may be applied in the case of the 

 Himalayas and Western China. 



Having interested myself in the problems here pro- 

 pounded during several years' travel in Western China, I 

 set to work to gather any facts whicli seemed to bear on 

 the problems of distribution ; and finding that the geo- 

 graphical features of the country can be largely traced to 

 comparatively recent geological changes, and that changes 

 of climate which must have taken place will all aff'ord 

 valuable evidence, I pondered over these matters too. No 

 doubt a complete understanding of all such contributory 

 factors will be necessary for a solution of the problem on 

 which I have embarked ; and to obtain the necessary 



