HOLE : SOME INDIAN GRASSES AND THEIR CECOLOGY. 35 



where the water supply is ample on account of percolation or otherwise but where the 

 light varies, and similarly a series of observations where the light is obviously ample but 

 where the water supply varies, and thus to assess separately the effect of each factor. An 

 interesting point arose in this connection with the observations carried out during the 

 present work regarding the effect of light on the development of Erianthus Ravennce. 



Several cases were noticed in coppice areas where the growth of this species was 

 obviously inferior and this was at first ascribed to the slight lateral shade existing in the 

 habitat. Further repeated observations showed that considerably denser shade than this 

 had no marked injurious effect provided ample water was available and the inferior growth 

 noticed was thus eventually shown to be mainly due to the drying of the soil by the numer- 

 ous superficial adventitious roots developed by the coppiced trees. Similarly it is quite 

 possible to arrange for a series of observations in nature in localities where the light 

 intensity varies greatly but where the temperature varies slightly and vice versa, although 

 the artificial isolation of these factors in experiments usually offers considerable practical 

 difficulties. 



While field observations can thus be arranged in such a way as to obtain information 

 regarding the individual action of each factor of importance, they offer this great advan- 

 tage over experiments that they enable information to be obtained regarding all the 

 factors of primary importance far more quickly than would be possible with experiments. 



The way in which the distribution of a particular plant depends in nature on a com- 

 plex of factors all acting together, so that in one place one factor is of dominant importance 

 and in another spot an entirely different factor, has already been briefly alluded to in 

 paragraph 28 above and from this it will be clear that whereas oecological observations in 

 the field can give us information, often very little less accurate than that yielded by experi- 

 ments regarding the individual action of isolated factors, they give us an incomparably 

 better idea of — 



(1) what factors are of primary importance in the case of any particular species, 



(2) what is the approximate degree of intensity of each such factor which in itself 



may suffice to cause obviously unhealthy or inferior growth of that species, 



and they thus enable us to explain the facts of plant distribution, to suggest suitable 

 methods of treatment calculated to improve the development of various species, to prevent 

 their diseases, or to decide on what species can be grown with most success in a particular 

 locality, far more rapidly and satisfactorily than can the results of a few experiments 

 dealing with the effect of one or two factors. 



32. It was therefore decided that the objects Lines of 

 of the proposed work in connection with forest grasses could be most satisfactorily 1 ^ L °sJ n dy°S ed 

 attained by— £ ores * 



J Grasslands. 



(a) Selecting a few important species of grass which are widely distributed and 

 which tend to be dominant over large areas. 



[ 35 ] 



