HOLE : SOME INDIAN GRASSES AND THEIR ONCOLOGY. 23 



quantity of moisture in the soil falls below a certain limit, the movement of water by capil- 

 larity in the soil becomes very slow. It is therefore conceivable that under these conditions 

 the roots of a mesophilous plant, in order to keep pace with the rapid transpiration from 

 the leaves, will remove water more rapidly from the soil than it can be replaced by capil- 

 larity. Vegetative activity would therefore obviously become impossible. A xerophilous 

 species on the other hand with its slower transpiration and absorption might be able to 

 continue activity. 



It is believed that the savannah grasses Saccharum Munja and S. Narenga, dealt with 

 in this paper, supply an illustration of the point here considered. The glaucous, wax-coated 

 leaves of the former are obviously xerophilous, while the dark-green leaves of the 

 latter are comparatively mesophilous. Notwithstanding this fact the former has frequently 

 been seen in the locality dealt with in this paper exhibiting more vigorous growth and 

 attaining larger dimensions than the latter. Plants of both species experimentally culti- 

 vated on loam, however, showed that, in February when the moisture-content of the surface 

 soil was comparatively small, although both species were growing under similar conditions 

 of soil and moisture, while S. Munja was growing vigorously (as judged by actual measure- 

 ments of the internodes of the culm), S. Narenga was vegetatively inactive. 



Warming rightly notes that " Tropical rain-forest constitutes the climax in the develop- 

 ment of vegetation for the whole world." 1 We may therefore accept the evergreen tropical 

 rain-forest, which Schimper classifies as a hygrophilous formation, as the most highly 

 developed cecological type of vegetation, the xerophilous as the least highly developed 

 and the mesophilous as an intermediate type. 



In view of the remarks made above, however, it is obvious that we must not depend on so-caiie<i 

 the so-called xerophilous and hygrophilous characteristics of plants as an unfailing criterion ami hygr o- S 

 of the type of vegetation to which they belong, but must consider them also in connection cilaracteris- 

 with periodicity and therefore regard them rather as an indication of the manner in which ^famii- 11 

 particular plants deal with the supply of water they are able to obtain, hygrophilous charac- ^"f^xero 

 teristics usually enabling a plant to deal with a large quantity of water in a short time and prions and 



-it m ■ • hygrophilous 



xerophilous adaptations enabling a plant to utilise its water supply slowly in small plants or 

 quantities. As the true criterion of a xerophilous or hygrophilous type of vegetation, vegetation, 

 however, it seems certain that we must consider the total quantity of moisture which plants 

 are able to utilise throughout their existence and this would be approximately indicated 

 by the vigour of growth and dimensions attained. On the whole it seems probable that the 

 best factor to accept would be the actual dry weight of organic material produced per unit 

 of area at the period when the majority of the individual plants composing the vegetation 

 have attained maturity. Thus for grassland the weight of dry grass, and for woodland 

 the weight of wood, per acre, would probably be an approximate criterion of most practical 

 utility, although strictly speaking the weight of subterranean as well as of aerial parts 

 ought to be considered and also the weight of the leaves and fruit produced by woody 



1 I.e., p. 340. 

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