The root development of plants and its relation to the amount and availability of soil moisture have been the subject of much study and speculation. Observations in California have yielded results which differ from conclusions drawn from some studies of similar nature elsewhere. Climatic conditions prevalent in California afford excellent opportunity for such study because the effective rainfall occurs almost entirely during the winter months and because soil-moisture conditions during a summer growing season are, in consequence, largely under control. Where the water table is far from the surface, experiments in California(14) have shown that the capillary movement of moisture is too slow to meet the needs of growing plants. Naturally then, roots must extend into a body of soil to utilize its moisture. Under these conditions, furthermore, direct evaporation causes material loss of moisture from only shallow depths of the soil, and moisture below 8 inches is lost by evaporation at an extremely slow rate, while plant transpiration accounts for the greater part of the water loss below this depth. It was, therefore, suggested(14) that the results of soil-moisture determinations, if made on adequate samples properly timed, would indicate the presence or absence of roots of plants growing on the soil. With soil previously wet, relatively dry soil below the surface layer would indicate the presence of roots. This paper presents some data in support of this suggestion. While it has to do with the development of the roots of grain-sorghum plants in relation to soil moisture, it is thought that the results obtained justify wider application.

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