PROSOPIS ^ 391 



the area of forest was at one time far greater, and that it has been gradually 

 curtailed by the extension of cultivation, a process hastened in recent times by 

 the development of irrigation. This curtailment is still proceeding rapidly, and 

 will continue to do so with the extension of irrigation, the natural dry forests 

 giving place to cultivation and irrigated plantations, chiefly of Dalbergia Sissoo. 



The five great rivers of the Punjab, of which the Indus is the chief, play 

 an important part in the origin and the distribution of the Prosopis forests. 

 These rivers, which are snow-fed, are liable to high floods when the Himalayan 

 snows melt in the hot weather, and the process of annual flooding with attendant 

 erosion and accretion proceeds in the manner already described for the Indus. 

 The topography of the plains thus exhibits four main stages in the alluvial 

 formation : (1) new alluvium in the river-beds ; (2) low land subject to inunda- 

 tion ; (3) higher ground beyond the reach of ordinary floods ; and (4) high 

 so-called bar land forming the watershed between the rivers. The subsoU 

 water-level varies from a few feet below ground surface in the low land near 

 the rivers to as much as 100 ft. on the high bar land. The soil is a deep fertile 

 loam with occasional hard pans of kankar, that is, concretionary calcareous 

 deposits, a few feet below the surface, and with occasional unfertile tracts of 

 saline soil locally known as reh or kallar. Prosopis regenerates on the low 

 ground subject to floods, but not on the high bar land, and it owes its existence 

 on the latter to the remarkable powers of survival due to its long taproot, 

 which responds to the lowering of the water-level, and to its capacity for 

 reproducing by root-suckers. Thus the conditions under which it is able to 

 persist when once established are entirely unsuitable for its reproduction by 

 seed, and it is further evident that this persistence may be of very long dura- 

 tion, perhaps, as Mr. Coventry remarks, for hundreds if not thousands ol 

 years. 



On the high bar land Prosopis trees are as a rule somewhat scattered, and 

 are usually associated with Salvador a qleoides and Capparis aphylla, while the 

 two latter species often occur without Prosopis, which has gradually dis- 

 appeared in course of time ; there are also frequently large blanks due to 

 deposits of kankar or the presence of saline soil. Except for the tree growth 

 the ground is bare of vegetation for several months in the year, though a fair 

 crop of grass is produced during the rainy season. On the lower ground 

 nearer the rivers the tree occurs gregariously in well-stocked crops ; here it is 

 sometimes associated with Tamarix and with Acacia arabica. 



In the Indian Peninsula the tree is not gregarious, but is scattered in open 

 dry types of forest in association with Acacia Catechu, A. arabica, A. leucophloea, 

 A. eburnea, Chloroxylon Swietenia, Anogeissus latifolia, Zizyphus Jujuba, 

 Z. Xylopyrus, and other species. In some localities it occurs on black cotton 

 soil with Acacia arahica and a few other kinds of trees. 



In the most important areas of its distribution the climate is dry to arid, 

 and is characterized by extremes of temperature, intense heat being a featiu-e 

 of the hot weather, while in the winter the thermometer may register a few 

 degrees of frost. Within its region in Sind and the Pimjab the absolute maxi- 

 mum shade temperature varies from 118 to 125 F., the absolute minimum 

 from 25 to 40 F., and the normal rainfall from under 3 in. to about 25 in. or 

 slightly over. In the Punjab plains it occurs most plentifully in the drier 



