THE WATER REQUIREMENT AND CELL‐SAP CONCENTRATION OF AUSTRALIAN SALTBUSH AND WHEAT AS RELATED TO THE SALINITY OF THE SOIL

Abstract

As carbon dioxid enters the stomata of a leaf to be subsequently absorbed by the moist cell walls surrounding the foliar air spaces, water evaporates from these surfaces and escapes to the atmosphere. This escapement of water is known as transpiration. The entire amount of water lost by a plant during Its growth may be taken into account and expressed as the ratio of the weight of water lost to the weight of dry matter produced. Values so derived are designated as transpiration coefficients or water requirements. The number of elements which go to determine the water requirement of a plant is by the nature of the measurement large, and the magnitude of the value obtained is dependent on all of the factors which have influenced the transpiration of the plant as well as on those which have in any way affected the absorption and fixation of carbon dioxid and its subsequent elaboration with other elements into the organic plant structure. The concentration of the tissue fluids of a plant is also subject to considerable variation. Not only are the concentrations different for different plants and different species but they differ with the habitat and appear to be largely influenced by the many changes which may take place within the immediate environment. While comparatively little is known concerning these fluids and the extent to which their composition and concentration are controlled by the surroundings or the part they play in fitting the plant to its environment, it is evident that their characteristics are of physiological significance. In this paper there are to be considered the results of a number of tests wherein the water requirements of plants grown on a series of soils successively more saline are compared with the concentrations of their tissue fluids. The experiments were planned to bring out such relationships as might exist between the water requirement of the plant and the concentration of the sap, and the extent to which either of these factors was influenced by the salinity of the soil. Two very different and in many respects well contrasted test plants were used. These were Australian saltbush, Atriplex semibaccata Brown (7); and wheat, Triticum vulgare Vell., variety Prelude. Investigators studying the water requirements of plants have frequently concluded that those conditions which are most favorable to the growth of the plant also favor lower water requirement values. While evidence