124 COMPOSITION OP FOREST CROPS. 



cial), and the bottoms of many valleys, as well as many low-lying 

 places, which always remain moist or wet in consequence of their 

 situation, and in which the soil is always deep, rich, and free, 

 thanks to the humus and vegetable debris continually washed 

 down from the higher surrounding ground. Even in the case of 

 such soils, it is desirable that the single species chosen to be raised 

 should be as shade-enduring as possible, so as to form a more or 

 less complete leaf-canopy. 



(ii) The effective factors of soil and climate should be uniformly 

 favourable for its prosperous vegetation over a more or less extended 

 area. Unless this area were absolutely large, the pure crop thus 

 composed could scarcely be considered more than a mere patch of 

 trees forming a small part of a much larger whole of truly mixed 

 forest. 



(iii) The produce furnished by the given species should either be 

 in such great demand that every square inch of the soil must be 

 devoted to its cultivation, or possess such a high market value that the 

 cultivation of any other species in mixture with it would result in an 



appreciable loss of possible revenue. 



The preceding three conditions would not unfrequently be re- 

 alised in certain stretches of sal forest, in tun plantations on 

 extremely favourable ground, &c. 



B. It has just been explained under what circumstances a 

 species may be grown pure. In the following case, and only in 

 that, there is no alternative but to raise pure forests : 



When the soil is such that no other species, whether marketable or 

 not, will grow on it ; for example, the stretches along the Indus, 

 which tamarisk or babul alone can occupy ; along streams at the 

 foot of the Himalayas, where sissu or khair only will succeed ; 

 some of the laterite tracts in Burmah, where eng is the sole tree ; 

 and so on. 



