MIXED CEOP or -UNrPOBM AGE. 33 



in the eng (Dipterocarpus tuherculatus) forests of Burtna the late- 

 rite keeps out, or restricts very considerably the distribution of> 

 other species. So in India where teak and Terminalia tomentosa 

 are companions, the proportion of teak increases as the amount 

 of clay in the soil diminishes, and vice versd, so that in strongly 

 clayey soils the latter species remains almost pure. Again, in the 

 very few instances in which sal and teak can grow side by side, 

 sal, possessing many conspicuous advantages, usually drives out 

 teak ; but generally there is a clear Hne of demarcation between the 

 two species, marked by an increase in the proportion of clay beyond 

 the point up to which sal can thrive. Then again, in the Boswellia 

 serrata forests of Central India that species becomes pure in fer- 

 ruginous soils. The more or less pure growth of sissu is also due 

 to the special nature of the soil. And so on. Even in a limited 

 area the soil may vary from point to point in respect of one or more 

 of its principal properties — physical and chemical composition, 

 depth, hygroscopicity, compactness— aU these various differences 

 favouring one species at the expense of another, besides producing 

 marked differences in the vigour of plants of one and the same 

 species. 



On shallow soils resting on a compact subsoil, surface-feeders 

 will thrive better than trees that send their roots deep into the 

 ground ; and, similarly, species that throw up suckers than others 

 not possessing that faculty, which, indeed, is increased in such 

 soils. 



The soil also influences reproduction to a very considerable 

 extent. If it is dry or hard or caked at the surface, species pro- 

 ducing seeds which germinate with difficulty (e.g., teak, &c.), or 

 are so large that they are either washed away or insufficiently 

 covered (teak, the Terminalia^), stand little chance against such 

 of their companions as produce smaller seeds that are caught in 

 little crevices or depressions (Anogeissus, Rhododendron, Pieris, 

 &c.), or seeds that germinate more readily (sal, &c.). Moreover 

 in such soils, species, the young seedlings of which develop a strong 

 taproot, capable of forcing itself into the ground (e.g. sal, teak, 

 Buchanania IcAifolia, Sec), are bound to prevail over their less 

 favoured companions. In loose, free, moist soil, ready germination 

 wiU not be a very great advantage, and the victory will depend still 

 less on the smallness of the seed. 



Lastly, we know that in the case of all deciduous hot-weather 

 leaf-shedders the persistence of the leaves depends on the quantity 

 of moisture in the soil, and it is evident that the longer a tree conti- 



