20 INDIAN FOREST MEMOIRS. 



fellings on hillsides and by subjecting woodlands in the plains to excessive grazing and 

 injury by fires. Similarly savannahs and steppes have in many cases undoubtedly resulted 

 directly from forest by fellings followed by fires and in some cases frost and excessive 

 insolation. 



It is of importance to realise this for it emphasizes the possibility of reconverting 

 desert, or grassland, to forest by the selfsame agency, viz. man, and shows that deserts and 

 grasslands need not necessarily be regarded as permanent on account of wide differences 

 in climate or soil. While we may therefore utilise such words as xerophilous and hygro- 

 philous as useful terms conveying some idea of the characteristics of a form of vegetation, 

 of some of the conditions of its environment and of the way in which the economy of the 

 plant is adapted to these conditions, we must continually guard against the idea that the 

 available water supply has necessarily been the dominant factor responsible for the exist- 

 ence and distribution of that type. In studying the cecology of any plant or plant-com- 

 munity, we must continually remember that its existence and distribution depend on a num- 

 ber of factors to each one of which the plant must be just as perfectly adapted as it is 1 to that 

 of water supply and that a slight change in any one of such factors may suffice to render 

 the continued existence of such a type impossible. If we wish to understand the cecology 

 of any plant, or plant-community, we must study, not only the adaptations of its vegetative 

 members, root, stem and leaf to the water supply, temperature, light, air currents, other 

 living plants and the animals of its environment, but also, no less, the adaptations shown 

 by the flowers and fruit and the arrangements necessary for the production of vigorous 

 seed and its suitable distribution, such as the season which various plants find most advan- 

 tageous for the production of flowers and fruit and the reason for this, 

 importance 21. A point that appears to be frequently 



of specific 



differences, overlooked in cecological work is that, although the nutrition of ordinary terrestrial plants 

 is carried out broadly on the same main lines, differences in detail undoubtedly exist. 

 There is reason to believe, for instance, that owing to a difference in the osmotic strength 

 of the substances produced in the cell-sap of the root-hairs some species may be able to 

 obtain sufficient moisture from concentrated solutions of salts, or from very retentive soil, 

 whereas others cannot do so easily, and the latter must therefore resort to devices which 

 aim at decreasing transpiration, the storage of water, and so on. If this is the case we 

 should naturally expect to find plants with, and without, obvious xerophilous adaptations 

 in the same habitat. The fact that Butea frondosa which is believed to possess no very re- 

 markable xerophytic adaptations can exist on saline soil and that it is in full vegetative 

 activity during the hottest dryest period of the year on the retentive Black Cotton Soil in 

 the plains of India possibly indicates some such peculiarity. The needs of different species 

 in respect of the quantity and quality of various mineral salts, of the quantity of oxygen 

 for respiration, of the intensity of light for assimilation and of temperature undoubtedly 

 vary considerably and we should therefore naturally expect to find considerable differences 

 in the nature and magnitude of the adaptations exhibited by different species in response 



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