MIXED CHOP OF UNIFORM AGE. 59 



and distribution of rain and dew, atmospheric humidity, intensity 

 and duration of sunlight, action of winds, and the depth, richness 

 and humidity of the soil. This being so, it is evident that in hilly 

 and mountainous country the influence of aspect is immense and is 

 often of itself great enough to determine the distribution of species. 

 In Southern Nimar, in the isolated block of hills known as the 

 Sambar Deo range, on the left bank of the Tapti, the southern slopes 

 bear Hardwickia binata, while the northern face being cooler 

 and moister, is covered chiefly with a dense teak copse, a rare 

 Hardwickia being visible here and there. In the outer North- West 

 Himalayas, Pinus longi/olia generally affects the warm southern 

 and eastern aspects, while oaks with rhododendron clothe the nor- 

 therly and westerly slopes. Nevertheless, lower down, where sal 

 and that pine meet, the latter, which is a tree of a colder climate, 

 is represented chiefly on northerly and westerly slopes, the sal 

 occupying the warmer aspects. Going up higher, into the region 

 of deodar, we find silver fir, spruce, Quercus dilatata, and semecarpi- 

 folia, with maples, birch, &c., predominating on cold northerly 

 slopes ; while deodar flourishes best on the sunnier aspects. We 

 thus see that a species is not always confined to the same aspects, but 

 may move from one to another as the altitude, in other and more 

 general terms, the temperature changes (see also next subhead). 



The aspect affected by a species may also vary with the amount 

 of atmospheric humidity of the localities in which it grows. Thus 

 in dry districts in Central and Southern India, the Dendrocalamus 

 Strictus affects the cooler northerly and westerly slopes ; whereas 

 in Bengal and along the foot of the Himalayas generally, where 

 the climate is damp, it is found chiefly on the warm southerly 

 faces of the lulls. 



In regions in which frost occurs, hardy species are favoured by 

 the conditions prevailing on southerly and easterly aspects, since 

 the rapidity of thaw on those aspects, due to the sudden action of 

 the early morning sun, aggravates the dangerous after-effects of 

 night frosts, which always occur when most of our forest species 

 are in active vegetation. We may hence find a species predomi- 

 nant on those aspects in one locality and slightly or not at all 

 represented on the same aspects in another, simply because frost is 

 seldom or not at all known in the one place while it occurs fre- 

 quently in the other. 



(e) Altitude. The main effect of altitude is to reduce tempera- 

 ture and also to increase thereby the humidity of the soil and the 

 atmosphere ; but it has, besides, the important effect of prolonging 



