HOLE : SOME INDIAN GRASSES AND THEIR CECOLOGY. 13 



13. It must be clearly understood that only inadvisable 

 after a far more detailed knowledge of plant-communities has been obtained than we at distinguish 

 present possess will it be possible to adequately appraise their relative importance and thus glcX Groups! 

 to evolve a really satisfactory classification and for this reason it seems impossible and 

 inadvisable to insist on any distinction at present between formation, association, and 



minor groups. All that seems immediately necessary is that those cecological groups which 

 exist and which can be readily recognised in different localities as distinct, either on 

 account of a different physiognomy, or habit of growth (tree, shrub, erect, climbing, etc.), a 

 different period of vegetative activity, of flowering or fruiting, a different admixture of 

 species, or on account of marked differences in the dimensions attained, in the density of 

 stocking, state of reproduction, and so on, should be separately described and, for the 

 present at all events, these may conveniently be termed communities. As our knowledge 

 increases these can be subsequently aggregated into larger groups or disintegrated into 

 smaller groups, as may seem advisable. 



14. Every type of vegetation is to a greater or Formations 

 less extent able to increase the quantity of soil available in a locality and to increase the necessarily 

 capacity of that soil for retaining moisture through the addition to it of humus. Rocks per 



are gradually weathered and broken up by the mechanical action of heat and cold and the 

 chemical action of the atmosphere and water. Plants also to some extent aid in 

 this work of decomposition by keeping the rocky surface moist, by the eroding action of 

 their absorbing roots and by the mechanical action of those roots which penetrate into cracks 

 and crevices and which by their continued growth are able to split the rock. Plants how- 

 ever are of still greater importance in this respect owing to their power of accumulating in 

 their neighbourhood wind and water-borne dust and debris and of resisting erosion. It is 

 thus clear that the continued existence of plants in a locality may alone be sufficient to 

 convert a xerophytic into a mesophytic habitat and the gradual covering of naked rock 

 with luxuriant vegetation through a succession of (1) Algse, lichens and mosses, (2) Xero- 

 philous grassland or woodland, and (3) Mesophilous grassland or woodland has been fre- 

 quently emphasized by cecologists. 



Again plants which are able to resist the injurious effect of a considerable degree of 

 shade and which are in consequence able to establish themselves on the ground already occu- 

 pied by other plants frequently have more moisture available for their growth and develop- 

 ment than those plants which establish themselves directly on bare unoccupied areas, 

 owing to the absence of shade and humus in the latter. 



Shade-bearing species therefore are frequently hygrophilous, or mesophilous, and are 

 able to enter into the composition of what must be regarded as a higher type of vegetation 

 than that which is usually constituted of light-demanders. 



A succession which thus proceeds from a xerophilous to a mesophilous and finally a Progressive 

 hygrophilous type of vegetation, i.e. from a simple to what must be regarded as a more 

 highly developed type, may be termed a 'progressive succession. Such a succession may 



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