INTRODUCTORY ESSAY. 97 



;etation of a different nature from any of i 

 in the extratropical regions of India during 



months only ; and 



b 



modifications 



climate for its presence. This consists of annual plants 

 the north temperate zone that do not appear within the 



), and 

 winter 



summer annuals 



are 



heat. These flower when the tropical plants 

 are very numerous, comprising many European and cosmo- 

 politan genera, and even species. Besides the winter crops of 

 the Gangetic plain, consisting of Wheat, Barley, and more 

 rarely Oats, with various kinds of pulse, there are, of wild 

 plants, Ranunculus sceleratus and muricatus, Capsella Bursa- 

 pastoris, Silene conica, Alsine media, Arenaria serpyllifolia, 

 Euphorbia Helioscopia, Medicago lupulina and denticulata, La- 

 thyrus Aphaca, Gnaphalia, Xanthium, Veronica agrestis and 



buft 



Heliotropium Europaum, various 



very many 



Myy 



ispus 



nunculus aquatilis, Lemna, and many others. 



The transition from the tropical to the temperate Flora 

 is more rapid in ascending above the level of the plains, 

 than in advancing northward at the same level; the change 

 of vegetation in a few thousand feet of ascent being much 

 greater than in as many degrees of latitude as would com- 

 pensate for the decrease of temperature experienced in that 

 ascent. In the perennially humid provinces of India the 

 climate of the base of the mountains is even more equable 

 than that of the adjacent plains, from the atmosphere being 

 more loaded with moisture. Hence in these regions a warm 

 temperate Flora (neither strictly temperate nor markedly tro- 

 pical) commences at elevations of 2-3000 feet, and prevails 

 over the nurelv tropical, which appears in scattered trees, 



pui 



o 



