INTRODUCTION 



THE botanical explorations carried on in China in recent years 

 make it possible to compare the forest flora of eastern con- 

 tinental Asia north of about lat. 22° 30' with that of eastern 

 North America north of the Rio Grande. In these explorations Mr. 

 Wilson has played an important part, and more than any other 

 traveller has shown us the remarkable richness of the flora of 

 western central China and the distribution and value of many of the 

 most important Chinese trees. A comparison of the flora of eastern 

 continental Asia with that of eastern North America made at this 

 time cannot be entirely conclusive, for although much has been 

 done to make known the Chinese flora much is still left undone ; and 

 there are still vast regions of the Celestial Empire into which no 

 botanist has as yet penetrated, and these may be expected to yield 

 new harvests of still unknown plants. 



It is not surprising that the forest flora of China is richer in 

 genera than that of eastern North America, for although the area 

 of the two regions under consideration is not very dissimilar there 

 is a great difference in their topography. In eastern North America 

 only a few mountain peaks reach an altitude of 6000 ft., and these 

 are wooded to the summit. In China mountain ranges are more 

 numerous, with peaks which sometimes rise far above the upper 

 limits of vegetation, and on some of these mountain ranges the 

 timber line is at least twice as high as the highest land in eastern 

 America. The connection of the great mass of mountains of 

 south-western China with the Himalayas which must be considered 

 their western prolongation, and the great tropical region which 

 extends uninterrupted by any large body of water southward from 

 south-western China, will account for the presence in the Chinese 

 flora of many Himalayan and tropical forms which have no counter- 

 part in eastern North America. On the other hand, the flora of 

 eastern North America has drawn from the large and arid plateau 

 of Mexico many genera of Cactacese, the Agaves, Yuccas, Dasylirion, 

 and other genera which have no representatives in China. While the 



