Physiological plant studies in South Africa Part I : wilting and osmotic phenomena of grasses and other plants under arid conditions

Abstract

A description of the meteorological, tellurical, and edaphic features of a typical farm in the semi-arid region of Bechuanaland is given, and the osmotic behaviour of the local flora recorded. The differences between suction force of grasses and of plants other than grasses are recorded in relation to soil moisture, atmospheric humidity, rainfall, and insolation. The phenomenon of wilting is explained upon the basis of the osmotic gradient between root and leaf, withering commencing in most grasses, under the conditions of soil and climate investigated, when the difference exceeds 0.2 molar sucrose. The local grasses display no morphological mechanism for protection against drought and show enormous variations in osmotic values. The other plants which survive throughout the year display various protective devices of an anatomical and physiological nature, and are characterized by high suction force. Those for which the lifecycle is confined to the brief rainy season of summer show low values incapable of much variation. Quantitative protocols are compared with figures on European plants and with the very scanty data available for arid regions in other parts of the world.