Excerpt from The Relation of Desert Plants to Soil Moisture and to Evaporation

Every observer of desert vegetation has had his attention drawn to the question of how certain plants of the arid regions are able to main tain a more or less active transpiration during long periods of absolute lack of precipitation, when the soil in which they are rooted becomes not only apparently air-dry but also attains exceedingly high tempera tures. It seemed that careful quantitative studies of the moisture con ditions in desert soil and desert atmosphere, and of the relation of these conditions to the transpiration and life of desert plants, might throw considerable light not only upon this problem of extreme xerophytism, but also upon the limitations of plant life in general. Just as the alpine summits of high mountains in all parts of the earth and the frozen tundras of the arctic regions exhibit vegetable life under temperature conditions which almost render it impossible, so the arid desert with its centimeters of annual rainfall and its meters of annual evaporation exhibits plant life under conditions of extreme dryness which similarly approach a limit to the very existence of such life. It is thus plausible to suppose that certain fundamental truths regarding the vital activities of plants may be more advantageously studied in the case of organisms existing under these extreme conditions than by confining attention to what are considered the more normal circumstances of life and growth.

With the aid of a grant from the Carnegie Institution of Washington the writer was able to spend the summer of 1904 at the Desert Botanical Laboratory of that Institution at Tucson, Arizona, in carrying out a series of quantitative studies on desert plants. The results of these studies are embodied in the present paper.

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