HOLE : SOME INDIAN GRASSES AND THEIR CECOLOGY. 19 



which are believed to owe their cecological peculiarities to a deficiency in the summer rain- 

 fall and to the fact that they must remain active through the winter to utilise the rain 

 falling at that season. Such plants are consequently supposed to be peculiar to regions 

 where rain falls chiefly in winter. Species of Ilex, Persea, Phoebe and Myrica however 

 all occur in India in regions where the rain chiefly falls in summer, the season when the 

 majority of the associated species show their maximum activity. The Sal tree also 

 curiously enough is practically evergreen and its foliage is unusually xerophilous for a 

 mesophilous species. It will also be noted that all the trees mentioned have a more or less 

 pronounced capacity for standing shade. No Forester doubts the extreme importance of 

 light as a factor capable of influencing the distribution of plants and, in the case of the Sal, 

 its capacity for withstanding a considerable degree of shade is almost certainly the factor 

 of most importance in enabling it to gain a footing in forests of miscellaneous species and 

 to form gregarious forests of its own. Diminution in intensity of light, however, must to 

 some extent mean less assimilation and therefore less vigour for growth and vital functions, 

 and from this point of view it can be understood why a plant, which has become adapted to 

 the utilisation of diffuse light and which has to compete in the struggle for existence with 

 plants which can utilise light of greater intensity, should find it advantageous to maintain 

 its foliage throughout the year. At the same time the fact that the foliage has to persist 

 through unfavourable seasons and withstand the cold of winter and heat of summer explains 

 why a somewhat xerophilous structure should characterise the foliage. The dominant 

 factor therefore which here seems responsible for the existence of a remarkable type of 

 vegetation appears to be not water but light. 



In this connection also it should be noted that there are several plant characters which Doubtful 



Adaptations. 



may be considered adaptations to deal with light or water. The highly polished surface of 

 many xerophilous leaves for instance may be of service in reflecting some of the incident 

 light, while, on the other hand, it may be of use in dealing with excessive moisture, in 

 causing the water to run quickly off the surface. A covering of pilose hairs is similarly 

 doubtful : — 



" The epidermal cells project as countless papillse which give to the leaf a velvety 

 appearance. Between the papillse the water rapidly spreads by capillarity 

 as a thin film extending over the whole leaf blade, so that the water can eva- 

 porate more quickly than if it were not thus spread out. The opinion has 

 also been expressed most recently that these papilla? serve to increase the 

 amount of light supplied to the leaf." 1 



20. Again, whatever may be the degree of ^ c a "°" f " e f n 

 adaptation exhibited by a formation to the conditions of moisture now prevailing in its habi- ^ rim ari / b r , e 

 tat, there is no doubt that in a great number of cases the dominant factor responsible for for the 



i i i n i i -it creation and 



the reduction of forest to bush and ot bush to virtual desert has been man, by reckless distribution 



of commnnl- 



1 Warming, p. 346. "~ tle3t 



[ 19 ] 



