1915-16.] BOTANICAL SOCIETY OF P^DINBURGH 5B 



the western, with perhaps some admixtureof North American, 

 forms westwards towards this gap, through wliich it liad 

 flowed southwards in company with the Himak\yan flora ; 

 and to this mingling of the floras, together with a good 

 climate, warmth, and rainfall, I chiefly ascribe the great 

 wealth of flora along the Burma-Yunnan frontier and the 

 rejuvenescence of Primula life there. There is every reason 

 to believe that the line of Primula migration was not across 

 Burma to Yunnan, but across S.E. Tibet, and it is on this 

 foundation-stone that I have built. Finally, I have suggested 

 that there is a remnant of the Sino-Himalayan range, now 

 severed by erosion from the Himalayas, left in the gap, and 

 that its flora will prove a real link between those of the 

 Himalayas and Western China. This remnant, which it is 

 my greatest ambition to explore, I place to the south of the 

 Sal ween sources in an unknown part of Tibet. 



The foregoing is a rough working hypothesis to account for 

 such facts as have impressed themselves upon me ; but it is 

 only with the object of furthering the investigation, in how- 

 ever small a degree, that I have ventured to put such im- 

 perfect notes in writing. Certainly the first criticism of every 

 botanist will be something like this : " Yes, but we would 

 like you to cite the distribution of, sa^^ one hundred plants 

 and show how that distribution agrees with the theory " ; or 

 perhaps : " Can you cite a reasonable number of Himalayan 

 plants and show that they are found on the parallel divides, 

 and a reasonable number which are found in your North 

 China area, left behind by the ice — for all would not have 

 been driven back by the ice — and a reasonable number of 

 American species also driven on to the parallel divides? 

 For without this last, what proof is there that the eastern 

 flora has ever driven back into the gap, by which means 

 alone could it have travelled southwards ? And if the two, 

 eastern and western, floras did not travel southwards in 

 company, does not the whole theory fail ? " 



These seem obvious criticisms, and I must confess to 

 being unable to cite individual plants which will prove 

 or disprove the theor}^ for the present. But at least I 

 believe the arguments to be not illogical, while they indicate 

 in which direction further research on the problem of the 

 Sino-Himalayan fiora is likely to be profitable. 



