1915-16.] IU)TANICAL .SOCIETY OF EDINBURGH 27 



of Saussurea (e.g.S. o^ra^/a^^a, Wall.) common to both divides. 

 But seeds only indirectly dispersed by wind (whether they 

 are small and light, like those of most Saxifrages and 

 Gentians, or heavier but shaken out of their capsules by 

 gusts of wind, like those of Meconopsis and Lloydia) could 

 not perform the journey from range to range \A'ithout first 

 establishing themselves in the valley ; and, apart from the 

 question of maintaining their vitality under these conditions, 

 once in the valley they would be beyond control of the 

 dominant wind capable of carrying them right across this 

 area, and under the influence of the strong desiccating up- 

 valley wind. Seeds which are normally dispersed by birds 

 are less common, and in this particular case, it must, I think, 

 be an occurrence so rare as hardly to merit attention. It is 

 ti^ue that Podophyllum Emodl, Wall, occurs both in the 

 Himalayas and on the Mekong-Yangtze divide, and it may 

 have been transported thither by birds. But the case seems 

 exceptional, for most of the plants with edible fruits in the 

 temperate rain forests of the Mekong-Sal ween divide, which 

 might be distributed by birds, e.g. species of Pyrus, Arisio- 

 lochia, Akebia, etc., are wanting on the Mekong- Yangtze 

 divide.^ However, the seeds of the majority of the plants 

 common to two or more of. the divides are neither such as 

 are transported by birds, nor such as are directly transported 

 by wind, but only shaken out of their capsules by gusts 

 of wind and spread over a limited area in the immediate 

 vicinity: for example, Priimda hella, Franch., and An- 

 drosace geranii folia, Watt, common to all three divides ; 

 Polygonum kermesinum, Ward mss., RJtododendron sp. 

 afF. Forrest a, Balf. f., L ilium giganfeum, Wall., and others, 

 common to the Mekong-Salween and Sahveen-Irrawaddy 

 divides ; Meconopsis pseiido-integrifolia, Prain, M. specwsa, 

 Frain, Primula li^cJiiangensis, G. Forrest, etc., common to the 

 Mekong-Salween and Mekong- Yangtze divides. Conversely, 

 many plants with seeds whirled freely into the air by wind 

 (e.g. many Conifers, species of Cremanthodium, Rhododen- 

 dron, etc.) are peculiar to one or other divide. Thus the 



' It is safe to assert tliat a plant is common to Ijotli divides if one has 

 found it on both. To assert, however, thai a plant is confined to one 

 divide is obviously unsafe until one has explored every inch of the 

 others. Such statements must therefore be regarded for the present as 

 only comparatively true. 



