HOLE : SOME INDIAN GRASSES AND THEIR CECOLOGY. 21 



to variations in the same factor. Very little is known about this and hence of the extent 

 to which structural differences can be relied on to give a correct conception of the intensity 

 of any particular factor of the environment, but we must obviously be prepared to find 

 plants with widely different adaptations existing together in the same habitat and forming 

 a part of the same community. 



22. Connected with the above question also me problem 

 is the possibility of precisely the same object, viz. successful existence, being attained in E^s^nce* ' 

 different ways by different adaptations. Some cecologists, for instance, do not admit that JJfJj; £ f 1 1 _ vcn 

 two plants, the one with an obvious xerophilous structure and the other with a hydrophilous J^^nn 

 structure, can arise through evolution in nature in the same habitat. Thus Clements ex- Jjjr^* 11 

 pressly states that " it is impossible for the same habitat to produce both hydrophytes and 

 xerophytes," 1 and he explains the well-known fact that many swamp species exhibit obvious 

 xerophilous adaptations by considering that the latter are stable structures which " were 

 developed when these species were growing in xerophytic situations, and not by the hydro- 

 phytic habitat in which the plants are found at present," 2 in other words he apparently 

 considers that such plants are not in complete harmony with their existing environment. 

 From what is known of the conditions of plant life and the universal perfection of the 

 adaptations developed by plants in response to their environment we should naturally ex- 

 pect that any species out of harmony with its surroundings would, if plastic, rapidly adapt 

 itself to those conditions, or that, if not plastic, it would fail to survive and would there- 

 fore not be found existing in nature under such conditions. If, on the other hand, a species 

 proves stable under different conditions of environment we should naturally be inclined to 

 think that no new adaptations are required, in other words that the existing structure is in 

 complete harmony with the conditions of the habitat. In the case of swamp plants for 

 instance the great difficulty in the majority of cases appears to consist in securing an ade- 

 quate supply of oxygen for the submerged roots. If the oxygen supply is short the normal 

 functions of the roots will' be depressed and a diminished water supply will result. This 

 can be met either by increasing the oxygen supply and thus the rate of absorption at the 

 roots, by the provision of more adequate aerating arrangements {e.g. wide air spaces, 

 pneumatophores, etc.) or by diminishing the loss of water by transpiration so that it may 

 keep pace with the slow absorption at the roots and thus there is no reason to believe that 

 plants, exhibiting xerophilous structures designed to diminish transpiration, are at all less 

 perfectly adapted to a swampy habitat, than are plants possessing hydrophilous arrange- 

 ments designed to increase the oxygen supply. Indeed of the two types of structure the 

 former is probably the most perfect and on the whole the most successful, inasmuch as it 

 may enable a species like Saccharum s'pontaneum to exist in a very dry and sandy habitat, 

 where there is a great scarcity of available moisture, in a heavy clay soil where there is at 

 some seasons a large quantity of water and little oxygen for the roots and at other seasons 



1 I.e., p. 1G9. 



2 I.e., p. 170. 



[ 21 ] 



