448 XXIII. LEGUMINOSAE 



limestone, conglomerate, and laterite, while as regards soil it is common on 

 sandy and gravelly alluvium, and on loam or gravel with varying proportions 

 of sand and clay ; it grows also on black cotton soil. It is frequent on arid 

 shallow stony soil and grows even on sheet rock. In the poor shallow soils 

 composed of murrain or kankar, which are frequent in parts of the Indian 

 Peninsula, it grows where few other species are able to survive ; this adapta- 

 bility is seen also in parts of the sub-Himalayan tract, where it grows pure, 

 though in stunted form, on poor hard soil composed largely of calcareous 

 nodules, where hardly any other tree can exist. On stiff clay where the drainage 

 is bad it becomes stunted and tends to die off early. 



Climate. Acacia Catechu is essentially a tree of comparatively dry regions, 

 though in its alluvial form it extends into regions of heavy rainfall, as in the 

 eastern sub-Himalayan tract, where it is found in places where the rainfall 

 is as much as 150 in. In gravelly riverain tracts, however, it has few com- 

 petitors and is no doubt enabled to establish itself for that reason. Away 

 from riverain tracts it occurs ordinarily in localities where the normal rainfall 

 varies from 20 to 85 in. In its natural habitat the absolute maximum shade 

 temperature varies from 105 to 120 F., and the absolute minimum from 

 30 to 55 F. 



Local occurrence. Suh-Hiinalayan tract. Acacia Catechu is common 

 throughout the sub-Himalayan tract from the Indus to Assam, ascending the 

 Himalayan valleys to 3,000 ft. and sometimes to 4,000 ft. From the Jumna 

 eastwards it occurs either gregariously in the beds of rivers and streams or 

 in various types of dry mixed forest, where it may be either more or less 

 gregarious or scattered. The riverain khair forests of northern India are very 

 characteristic. They spring up on new alluvium along the banks or in the 

 beds of the rivers and streams in the valleys of the outer Himalaya and the 

 Siwalik range, on deposits of sand, shingle, and boulders, extending some 

 distance out into the plains provided the alluvium remains sandy or shingly 

 and does not reach the consistency of soft mud. In these alluvial forests the 

 khair is either pure or mixed with Dalbergia Sissoo, and occasionally with 

 Acacia eburnea, Bombax malabaricum, Albizzia procera, and a few other species. 

 It is also associated with characteristic grasses, the chief of which are Saccharum 

 Munja, S. spontaneum (xerophilous form), Aristida cyananiha, Triraphis mada- 

 gascariensis, and Andropogon monticola. There is often a dense undergrowth 

 of Adhatoda Vasica in these riverain forests. The gregarious habit of the tree 

 in this type of forest is shown in Fig. 169. 



At the higher elevations it meets the hill species ; for example, above 

 Ratighat in the Naini Tal hills, at 4,000 ft., it grows in a river-bed with 

 Quercus incana and Pinus longifolia growing on the slopes down to the edge 

 of the river : in the same locality it is found mixed with Celtis australis on old 

 riverain boulder beds. 



In non-riverain tracts the tree occurs either in scattered savannah lands 

 or in various types of dry mixed forest, sometimes as a survival from former 

 riverain forest which has become elevated at no very distant date above the 

 river-bed owing to changes in the course of the river, but frequently on land, 

 both flat and hilly, which shows no such recent transition, or on which it has 

 sprung up naturally after the land has ceased to be new alluvium. In such 



