A long series of investigations carried out over a wide geographic range has shown that the physico-chemical properties of leaf tissue fluids vary from habitat to habitat in correlation with environmental conditions. An outline of problems was drawn some years ago (Harris 'I7) and a brief review of results has been given as an introduction to a recent investigation of the vegetation of Tooele Valley, Utah (Harris et al., '24b) and in explanation of the application of tissue fluid studies to agricultural problems (Harris et al., '24a). The mass of evidence now accumulating tends to show that the differences demonstrable in the tissue fluids of plants of various habitats are in part due to innate differentiation of the species and in part to direct influence of environmental conditions. This is clear from unpublished work on various wild species growing under diverse environmental conditions and has been established experimentally for small cultivated tracts by investigations on the variation and differentiation of Egyptian and Upland cotton (Harris et al., '24a). The investigations of Cavara ('05) and Fitting ('II), and subsequent studies by our coworkers and ourselves, have shown that plants growing under saline conditions may be characterized by enormously high osmotic concentrations. We have noted, for example, that during periods of drought Atriplex confertifolia and Atriplex nuttallii may exhibit concentrations far above ioo atmospheres (Harris et al., '2I) . It seems probable that ions absorbed from the soil contribute largely to the development of such concentrations. In the analysis of the variables to which differences in osmotic concentration are due it therefore becomes of great importance to determine by precise analytical methods the concentration of various ions and of inorganic and organic molecules in the plant tissue fluids. Because of their widespread and abundant occurrence and high solubility chlorides seem one of the most important constituents to be determined. While a score or more papers on the detrmination of chlorides in blood and urine have been presented by biochemists and animal physiologists, and while one of these methods has been modified with a view to fitting it for
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Lawrence et al. (1925) studied this question.