THE ECOLOGY OE THE UPPEE GANGETIC PLAIN. 309 



striking changes in the aspect and content of the vegetation from sea- 

 son to season, and may be called seasonal succession. As a result of 

 the three well defined climatic seasons, rainy, cold, and hot, there are 

 three equally well marked vegetational seasons. The traveller across 

 the Gpper Gangetic Plain is impressed with the numerous groves of 

 stately trees. These groves are without exception planted, and are 

 composed of species that either are not native to the immediate area 

 or that cannot survive in the young stages without protection. Some 

 of these trees would quite readily perpetuate -themselves were it not 

 for the pressure of the human factors. 



Aside from cultivated fields and the groves of planted trees, the 

 aspect of most of the area is determined by herbaceous plants. Here 

 and there are tracts dominated by shrubs and small trees, but across 

 these the herbaceous vegetation extends unchanged. Obviously there 

 is no change in the content of the woody vegetation in response to 

 change in season, but there is response in the matter of leaf fall and 

 time of blooming. Even these changes are relatively inconspicuous 

 in comparison with the changing aspect of the herbaceous and under- 

 shrub vegetation. It is periodicity in the small and very abundant 

 annual and perennial plants that renders the fact of seasonal succes- 

 sion so conspicuous. 



During the rainy season, when all conditions are favorable for 

 maximum plant growth, the whole country is covered with a luxurienfi 

 mantle of herbaceous vegetation. Much of it is annual. The 

 perennial herbs and undershrubs attain their maximum development 

 at this time. The vegetation approaches hygrophytic, with large soft 

 thin leaves and tender stems. It is during the rainy season that the 

 tropical aspect of the flora as well as its composition appears most 

 clearly. 



With decrease of rain, and the lower temperature of the cold 

 season, much of the rank growth of the rainy season disappears. 

 What survives is gradually eaten down by grazing animals. The 

 hygrophytic annuals are replaced by mesophytic annuals, especially 

 Compositae, of more temperate connections. Perennials lose their 

 lu&urient tropical appearance, and in every way the vegetation is less 

 in amount, number of species, and conspicuousness. 



With the advent of the hot season, the high temperature 

 and extreme aridity complete the destruction of the annual vege- 

 tation that is not situated in favored edaphic spots, and little 

 more than the persistent perennials remain. There are a few 

 annuals, but the number is small. The perennials now present a 

 very different appearance from that of the rainy season, and even 

 the cold season. All but the youngest leaves fall, and the more deli- 



2563—40 



