1915-16.] BOTANICAL SOCIETY OF EDINBURGH 49 



I have already referred to the expansion of the Himalayan 

 Primulas as the Burma-Yunnan area is reached ; in no 

 sections is this more prominent than in sections SufFruti- 

 cosa, Muscarioides, Sikkimensis, and Omphalogramma, none 

 of which have representatives in the North China area ; but 

 it is equally conspicuous in the sections Candelabra and 

 Nivalis, each of which has a single representative in North 

 China. The two last named are widely distributed — the 

 Nivalis section is universal through P. nivalis, Pallas, 

 itself ; however, the first four named seem to have origi- 

 nated in the Himalayas and thriven in the Yunnan area ; 

 at least they are found nowhere else. One section, Auri- 

 culata, confined to North China so far as the three areas 

 under discussion are concerned, is well represented outside 

 China, and suggests in its distribution that the North 

 China area may have been peopled from North Central 

 Asia as well as from the Himalayas, driven thither south- 

 wards by the ice. But § Auriculata is nearly related to 

 § Farinosa, a typical American section with representatives 

 also in Japan, so that we have here in these two sections 

 evidence for that westward movement of the flora from 

 America, via Japan, already referred to ; or possibly Auri- 

 culata came from Europe. Anyone who has followed the 

 argument so far will now see why it is that the Himalayan 

 flora is richly represented in Yunnan, but poorly in Western 

 Burma and North China. As Sir George Watt remarks, 

 the forms abundant in Sikkim and Bhotan attain their 

 greatest development in Yunnan ; but evidently not across 

 Assam and Burma from the west, as might seem the most 

 natural route considering tiie trend of the Himalayas, a 

 prolongation of which in the same direction would cross 

 the richest Primula area in Yunnan. On the contrary, the 

 alpine flora of N.E. Burma which penetrates southwards 

 to within a degree or two of the Tropics has travelled right 

 round in a vast semicircle from the east end of the 

 Himalayas via the mountains north of the Irrawaddy 

 sources, and may possibly still be in communication with 

 the supply. I think there can be no doubt on this point 

 from what I have said on the flora of the parallel divides, 

 evidently derived from a common source, and from the 

 fact that near Hpimaw (lat. 26° N.E. frontier), on the 



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