are high enough to rise above the snow* line, the whole range of the flora, from the foot 

 of the mountains to the snowline can survive. This probably is one of the main causes 

 which accounts for the greater richness of the Chinese flora, as contrasted with that of 

 eastern North America (see Sargent): the Chinese mountains around the Yangtse 

 Valley are enormously higher than those of the eastern United States. 



Reference to Mr. E. H. Wilson's zonal tables of the Chinese flora (op. cit. vol. II, 

 pp. 5—9), and to the records of herbarium specimens, especially to the great collections 

 of Dr. Augustine Henry, in which habitat is so carefully given, shows that the congeners 

 of the Reuverian are mostly inhabitants of the temperate zone of the mountains of 

 Western China, and to a smaller degree of the coobtemperate zone of higher altitudes. 

 A few are warm temperate or even subtropical forms of the valley floor; but the general 

 facies is decidedly temperate. 



The fall of temperature in Limburg from the Reuverian to the Glacial Period 

 corresponds approximately with the temperature gradient from the valleysfloor up to 

 the temperate mountain zone, still inhabited by the Reuverian representatives in the 

 Yangtse district today. We take this to imply that during the Glacial Period the Reuverian 

 element of the Chinese flora occupied the valley ^bottom, but as the climate grew warmer 

 this flora was driven up the mountains to 1500 or 2000 metres, leaving the valleysbottom 

 to some extent depopulated. With each return of glacial or interglacial conditions the 

 same process would be repeated. Remembering that we ourselves are now living in a 

 genial climate, following a rigorous one; conditions which, we suggest, would in a flat 

 country or valleysfloor correspond with a poor flora, it is interesting to note what 

 Mr. Wilson says of the flora of the comparatively low4ying Red Basin of Szechuan 



(op. cit. vol. 1, p. 65) "the flora, in contradistinction to that of the contiguous regions, 



is relatively poor, and the species largely common to the entire basin. Further, the 

 majority of these species are widely spread throughout the warmer low4evel regions 

 in China, some indeed ranging to the extreme eastern limits of the country." If we are 

 right in thinking that this warm*temperate and subtropical flora has had to be re* 

 introduced since the last Glacial Period, this is exactly what we should expect. The 

 valley^floor of the Szechuan basin is only now being re^peopled from the south by way 

 of the coastal plain, after having been deserted by the flora which occupied it during 

 the Glacial Period. 



With regard to the relationship between the Reuverian, the living Chinese, and 

 the American floras, before leaving the subject we may again refer to Mr. Wilson, 

 one of the greatest living authorities on the flora of China. He writes (op. cit. 

 vol. II, pp. 11, 12): — 



"At first sight it would very naturally be supposed that the Chinese flora was 

 most closely allied if not to that of Europe at least to that of the Asiatic continent 

 generally. Yet this is not so. The real affinity is with that of the Atlantic side of the 

 United States of America! 



"This remarkable fact was first demonstrated by the late Dr. Asa Grey when 



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