THE FLORA OF WESTERN CHINA 13 



from any other region in the world. In others, — for example, 

 Oak, Hornbeam, Elm, Birch, Ash, Beech, and Sweet Chestnut, 

 — where the families range around the whole temperate zone 

 of both Old and New Worlds, the individual Chinese species are 

 usually more closely akin to those of North America than to 

 those of Europe. 



The explanation of this phenomenon is to be found in the 

 glaciation of the Northern Hemisphere in prehistoric times. 

 In those far-off times the land connexion between Asia and 

 North America was far more complete than it is to-day, and 

 the flora extended much farther to the north. The ice-cap 

 which gradually crept down forced the flora to travel towards 

 the equator. Later, when the period of great cold was over, 

 and the ice-cap receded, the plants crept back ; but the ice-cap 

 remained at a more southern latitude than before, and conse- 

 quently rendered much of the land formerly covered with 

 forests too cold to support vegetable life of any sort. This 

 rearrangement after the Ice Age caused a break between the 

 two hemispheres, and the consequent isolation and cutting 

 off of the floras. Other agencies and factors played a part, 

 but the above explains briefly and roughly why the floras 

 so much alike should to-day be so widely separated geo- 

 graphically. 



That the Chinese flora is an ancient one is evidenced by 

 the number of old types it contains. For example, in ancient 

 times. Ginkgo hiloha (Maidenhair tree) was found, not only in 

 Asia, but in Western Europe, Northern California, and Green- 

 land, as the fossil remains found in Jurassic beds of these 

 countries testify. To-day it exists only in China and Japan 

 as a cultivated tree, being preserved to us by the Buddhist 

 and other religious communities who plant it in the neighbour- 

 hood of their temples. Cycas, Cephalotaxus, Torreya, and 

 Taxus are other old types, but these occur in a wild as well 

 as in a cultivated state in China to-day. Many of the older 

 ferns, such as Osmunda, Gleichenia, Marattia, and Angiopteris, 

 are common in China and widely spread. In speaking of the 

 older ferns it may be of interest to note that Augustine Henry 

 discovered in Yunnan an entirely new genus of Marattiacece, 

 which has been named Archangiopteris. 



