220 



Supply of 

 Moisture. 



and calcium and salts of iron often appear to be injurious in this 

 way. Plants, however, vary greatly in their power of with- 

 standing such injurious influences, and while some plants can 

 thrive on a saline, or calcareous soil, others cannot exist there, 

 a fact which is largely responsible for the characteristic vege- 

 tation of such soils. Among important Indian trees, Butea 

 frondosa is remarkable for being able to grow on soil contain- 

 ing large quantities of salt. 



Supply of A su pply of x yg en being essential for the healthy action of 



Oxygen. the roots of plants, the water in the soil must be well aerated and 

 hence not stagnant. Many of our Indian trees are exceedingly 

 sensitive in this respect and cannot exist unless the subsoil is 

 well drained. The Deodar, Pinus longifolia, Sal, and many 

 others, all require well- drained soil. On the other hand, many 

 species can thrive in water-logged localities, e.g. Butea frondosa, 

 Terminalia Arjuna and others. 



The physical and chemical properties of the soil itself, and 

 of the subsoil, influence the amount of available moisture to a 

 considerable extent. Finely divided soils, such as clays, have 

 the greatest power of absorbing water, and also, being very 

 impermeable, of retaining it. Sand on the other hand, being 

 very permeable, can retain very little water. Calcareous soils 

 again have very little power of absorbing water, while those 

 with an admixture of humus are capable of absorbing and 

 holding large quantities of water. Among Indian trees which 

 thrive best on clayey soils the well-known Sain, or Saj 

 (Terminalia tomeniosa), may be mentioned. Among trees often 

 found on calcareous soils are Khair (Acacia Catechu) and Satin 

 Wood (Chloroxylon Swietenia)., but the fact that both these trees 

 are commonly also found on non-calcareous sand, and on other 

 soils in dry forests, indicates that the important factor in this 

 case is the small amount of moisture in the soil and not the 

 Characteris- P resen ce of a particular chemical constituent. Two very 

 tics of characteristic and widely distributed types of Indian soils require 

 Laterite and b r i e f mention here, viz. (1) Laterite and (2) Regur, generally 

 known as Black, or Cotton, Soil. The first is remarkable for its 

 very low capacity for holding water and for containing a large 

 percentage of iron. The Eng, or In (Dipterocarpus tuberculatus), 

 a valuable timber tree of Burma, is almost exclusively found 

 on laterite. Many other species, often found on laterite, 

 occur just as frequently also on other dry soils. Regur is 

 generally found in the neighbourhood of trap rocks and con- 

 sists largely of clay with a considerable admixture of organic 



