MIXED CEOP OT rNIPOEM AflE. 



57 



Doubtlessly the natural spread of sissu south of its range is 

 limited by the drier atmosphere of the adjoining region. Prosopis 

 spieigera, Capparis aphylla, and many other plants of Rajputana 

 and the Punjab plains require less atmospheric humidity than most 

 other Indian species. Trewia nudijlora is confined only to tracts 

 visited by moist sea-breezes or to the vicinity of the Himalayas 

 from the Jumna eastwards, where the the air is always compara- 

 tively moist. The very high relative humidity of the inner ranges 

 of the Himalayas enables evergreen species to prevail there, not- 

 withstanding the low rainfall they receive. 



The abundance and continuousness of rain at the beginning of 

 the rainy seasou exercises a very strong influence on the germina- 

 tion of the seeds of the various species. The seeds of some species 

 have to go through a protracted process before they become perfect 

 plants. A sudden break in the rains, and a few hours of strong 

 sunshine before the process is complete, might kill the majority of 

 such germinating seeds. This happened over several square miles 

 in the Khandwa Reserve in Nimar in the Central Provinces, in 

 1879, in the case of the Hardwickia hinata. Seeds of other species 

 again, such as the Terminalias, teak, &c., require a large quantity 

 of moisture to germinate, and hence their inability to extend into 

 very dry districts, where otherwise circumstances are favourable for 

 their growth and fructification. Moreover above the 20th. parallel 

 of latitude in India proper, if the summer rainfall is at first short, 

 and the seeds of such species can consequently germinate only in 

 the latter half of the season of vegetation, the young herbaceous 

 plants must fall easy victims to the hot sun of October and Novem- 

 ber and the frosts of December and January. 



Lastly, it may generally be said that those species, the seedlings 

 of which develop a long powerful taproot, will withstand more severe 

 and continued drought and may thus survive where others, less 

 favoured in this respect, will die off in numbers or even entirely 

 disappear. 



Besides influencing the growth and soundness of individuals of 

 the various species, the amount of atmospheric moisture affects also 



