48 INDIAN FOREST MEMOIRS. 



rapidly dried after rain owing to poor capillary action, the oxygen content being apparently 

 too small for Saccharum Munja and the water content too small for Erianthus Ravennce, 

 these species therefore being unable to oust the less vigorous plant. On the other hand 

 Imperata is able to thrive and attains its maximum dimensions in a typical swamp, where 

 neither of the larger species can penetrate. 



This has already been alluded to in paragraph 22 above, where attention was drawn 

 to the fact that one and the same species may frequently be found to thrive well on a 

 physically dry soil, such as a sand or dense clay, and also on a physiologically dry soil, 

 such as the saturated, water-logged soil of a marsh. Notwithstanding the fact then that 

 intermediate forms occur, partly on account of the gradual shading away of the environ- 

 mental factors and partly on account of the fact that one and the same species may occur in 

 different habitats and communities, field workers will, it is believed, readily admit that the 

 four main types of grassland indicated above can be easily distinguished and that they 

 are separated by real differences, both as regards the conditions of the habitat and the 

 characteristics of the vegetation. 



43. Turning now to the woodland com- 

 munities, the Forest Officer will, it is believed, readily admit the importance 

 of selecting and describing types, even though these be connected more or less 

 completely by intermediate forms. Thus, although four of the seven species given 

 for community No. I are commonly found also in No. II, there is a real difference 

 between the open crop of No. I with more or less isolated clumps of Zizyphus, 

 Adhatoda, Acacia and Dalbergia, with bare spaces occupied by the shrubs Calotropis and 

 Orthanthera and with scattered tufts of xerophilous grasses, on the one hand, and the more 

 or less close crop of the dry miscellaneous forest forming type No. II on the other hand, in 

 which a number of additional species have appeared. 



Similarly there is an undoubted difference between Nos. II and IV although many of 

 the species found in the former also pass into the latter. In IV, however, there is an 

 obvious preponderance of species which require a larger quantity of available moisture and 

 which are not found in No. II. 



Again, although many of the species characteristic of No. IV occur also associated with 

 Sal, there is no difficulty in distinguishing No. Ill in which the Sal is always the dominant 

 species as a distinct type. Just as in the case of grassland, so here also we have species like 

 Bombax malabaricum and Garuga pinnata which grow well in physically dry soil and also 

 in heavy wet soils and species like JEgle Marmelos which thrive on dry sandy soil and also 

 on hard clay. 



The Forest Officer has long recognised this fact that certain species occur in very 

 different habitats in distinguishing what he calls indicating species, or indicators, which 

 are, as a rule, only found in places where a particular soil occurs, where a certain quantity 

 of moisture is available, or where a particular intensity of light prevails, and which thus 

 indicate the existence of certain factors and their intensity, from those termed indifferent 



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