1915-16.] BOTANICAL SOCIETY OF EDINBURGH 9 



the instrument gives no indication of the rate of transpira- 

 tion of any plant ; it only measures the humidity or dry- 

 ness of the atmosphere, thus corresponding more to a 

 hygrometer. 



On examining the tables it will be seen that wind is of 

 more importance than high temperature or sunshine in 

 accelerating evaporation. For example, in Table I the 

 average rate of evaporation for six days, recorded as " light 

 breeze" is 1"63 mm. per hour, and that for four days 

 recorded as "fresh breeze" is 1'64 mm. per hour, though 

 in the former case sunshine is recorded as " continuous " for 

 all six days; in the latter case it is recorded as "intermittent " 

 on three out of the four days. Similarly the average 

 maximum temperature for the six days was 68-7° F., as 

 against only 67"5° for the four days. Again in Table II, 

 July 4-5, the rate of evaporation during the night is 

 significant, as is the rate on June 23 after sunset. 



At Doker-la, on the Mekong-Salween divide, the humidity 

 of the atmosphere, owing to the perpetual drizzle, greatly 

 retarded evaporation. The weak points in the tables are 

 of course the small number of observations recorded, the 

 fewness of the stations (though the main ones are dealt 

 with), and the fact that the evaporimeter was not exposed 

 between the same hours each day, nor for the same number 

 of hours. However, theiinal figures, 10 : 71 : 2-4, probably 

 give a fairly correct idea of the comparative rates of 

 evaporation (and hence condition of the atmosphere) at 

 these three places, from which we may infer that wind 

 and rainfall are the most important factors in determining 

 the dominant formation, soil and situation being auxiliary 

 factors, helping to control the incidental formations and 

 select the flora. 



We come now to a detailed consideration of the com- 

 position of the various formations and plant associations 

 mentioned, and first let us take the temperate rain forest, 

 the dominant formation of the Mekong-Salween divide. 



The conifers are Cunninr/Jiamia^?), Taxus, Picea, of 

 great size (one I measured was 19 feet in girth, 5 feet 

 from the ground), Abies, Pinus (2 species), and one I could 

 not identify. 



Amongst the deciduous-leaved trees are species of Pyrus, 



