14 TRANSACTIONS OF THE [Sess. lxxx 



block to the student of distribution, and it is evident that 

 we should not find plants common to the Salween-Irrawaddy, 

 Mekong-Salween, and Mekong- Yangtze divides if the pre- 

 sent ph^'sical features obtained when the distribution took 

 place. Hence, rather than argue that because the mountain 

 systems are connected (which they are not) therefore the 

 floras are similar, we must recognise that because the floras 

 are related, therefore the mountain systems must once have 

 been in closer connection than they are at present. 



So much for the main problem. Once we have unravelled 

 this previous continuity of mountain systems, few direct 

 traces of which are left, we may find other diflSculties 

 cleared up also. 



A question which many English horticulturists who — 

 thanks largely to the public spirit of Messrs. Veitch of 

 Chelsea, and Bees, Ltd., of Liverpool, and to the French 

 Catholic priests before them — have gained some insight into 

 the almost limitless wealth of flora in Western China, are 

 asking themselves is : Whence comes this unparalleled 

 wealth, which (as the acute Sir Joseph Hooker long ago 

 prophesied it would — a prophecy amply borne out during 

 the last two decades by a dozen collectors) more than rivals 

 that of Sikkim ? 



A critic of mine in the Gardeners' Chronicle, reviewing 

 a book ^ I wrote, in which attention was drawn to tlie sub- 

 ject, answered this question apparently to his own satis- 

 faction. I must say I thought the explanation rather 

 lame, and moreover the writer was wrong in his facts. 

 But the real inadequacy of it lay in the fact that he 

 altogether ignored the effects of plant migration and mix- 

 ing, and it is on this fact that I am myself inclined to lay 

 great stress. Briefly, if we can find a satisfactory ex- 

 planation for the close relationship existing between the 

 Himalayan and Chinese floras, I believe we shall have gone 

 a long way towards explaining the wealth of the Chinese 

 flora, to account for which secondary factors, such as 

 abundant rainfall and richness of soil, are quite insufficient. 



Closely coiniected with the above is the special question, 

 to which I shall revert later, Why does the genus Primula 



1 The Land of the Bhie Popjjj : Travels of a Naturalist in Eastern 

 Tibet, by F. Kingdon Ward, B.A. (Cambridge University Press, 1913). 



