Page:Provincial geographies of India (Volume 1).djvu/91

 Affinities of Panjab Flora.— It is hopeless to describe except in the broadest outline the flora of a tract covering an area of 250,000 square miles and ranging in altitude from a few hundred feet to a height 10,000 feet above the limit of flowering plants. The nature of the vegetation of any tract depends on rainfall and temperature, and only secondarily on soil. A desert is a tract with a dry substratum and dry air, great heat during some part of the year, and bright sunshine. The soil may be loam or sand, and as regards vegetation a sandy desert is the worst owing to the rapid drying up of the subsoil after rain. In the third of the maps appended to Schimper's Plant Geography by far the greater part of the area dealt with in this book is shown as part of the vast desert extending from the Sahara to Manchuria. Seeing that the monsoon penetrates into the province and that it is traversed by large snow-fed rivers the Panjab, except in parts of the extreme western and south-western districts, is not a desert like the Sahara or Gobi, and Schimper recognised this by marking most of the area as semi-desert. Still the flora outside the Hills and the submontane tract is predominantly of the desert type, being xerophilous or drought-resisting. The adaptations which enable plants to survive in a tract deficient in moisture are of various kinds. The roots may be greatly developed to enable them to tap the subsoil moisture,