HOLE I SOME INDIAN GRASSES AND THEIR CECOLOGY. 41 



surface is readily replaced by capillarity. Both as regards supply of mois- 

 ture, degree of soil aeration and temperature, therefore, this type is interme- 

 diate between I and II. 



39. The above types have, as a rule, been 

 clearly distinguished by practical Forest Officers and, in Working-Plans, I and II are 

 usually described under the name of the recent or low alluvium and III under the name of 

 the old or high alluvium. 



From the explanations given in paragraph 7 above it will be seen that II is a typically 

 xerophvtic and III a mesophytic locality. I is probably on the whole mesophytic although 

 for some types of vegetation it is hygrophytic. 



The terms old and recent are apt to encourage the deduction that there has been in 

 every case, as regards the cecological characteristics of the soil, what may be called a develop- 

 mental, or progressive, succession of the same type and which has gradually resulted in the 

 conversion of the recent, or low alluvium, into the old, or high, alluvium. 



To a great extent this is probably true, but it is obvious that we must clearly distin- 

 guish two main types of succession, viz. : — 



(1) That in which water-logged soil, usually containing a large admixture of clay, 



becomes converted into well-aerated moist loam by a lowering of the water- 

 table and addition of humus. 



(2) That in which dry sand becomes converted into moist loam chiefly through the 



addition of humus. 



It is equally clear that we must recognise the possibility of a regressive succession, 

 such as might arise for instance through the clearing of the forest growth and cutting off 

 the supplies of humus. 



Mr. Millward 1 in an interesting paper has emphasized the fact that, according to 

 their mode of deposition, in still or running water, soils differ ab initio essentially in their 

 quality and composition owing to the size of the constituent particles, on which the distinc- 

 tions between gravel, sand, loam and clay depend. Consequently bare unoccupied areas of 

 soil of the same age may become available for the first time for plant colonisation which 

 may vary from practically pure clay to coarse gravel, and the fact that the heavy soil in 

 this locality is now chiefly found on the higher slopes and plateaus is probably due to its 

 having resisted erosion better than the light sandy soils. 



It is important to realise these points, inasmuch as changes in the cecological character- 

 istics of the soil are directly connected with the succession of different types of vegetation, 

 and it has already been explained in the footnote to paragraph 14 above that, as regards 

 the most important type of vegetation in the locality here dealt with {viz. Sal forest), we 



1 Indian Forester, Vol. XXVIII, p. 411. 



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