1. The variation of the foliar water content as related to the wilting of plants was studied by determining the water content at the critical stages of wilting of leaves, Coleus Blumei, Glycine Soja and Mimosa pudica being used as the materials for experiments. 2. As the index to show the water content of leaves, not only its percentage values on the basis of the fresh and dry weight also the amount contained in the unit area of the leaf were determined. The content per unit volume of the tissue powder was also attributively determined. However, it was proved, that the area method was preferable to the percentage methods. The consideration of results was made therefore principally on the values obtained by this method. But in the case of Mimosa, where this method was impracticable, the values obtained by the dry weight method was applied. The powder method was also proved to be a good applicable one. 3. The water content of leaves of a plant seemed to be very alike at a given critical stage of wilting, for instances at the beginning of wilting or at the point of so-called permanent wilting of a plant. But this value was affected not a little by the culture conditions. The higher the water holding capacity of culture soils, the larger was the critical water content of leaves of Glycine, while the results found in Coleus were the opposite. This relation was assumed by the writer to have some bearing on the xerophytic nature of plants. 4. The water content of leaves at the critical wilting point of different plants was proved very different to each other. The ratio of this critical water content to the content at the stage of full turgidity was also very different one from the other. The value of this ratio was found much higher in Coleus than in the other two materials, while the values for these latter two were near to each other. 5. The ratio in question seemed moreover to be specific to a given plant, and to show the degree of the resisting power of a plant to wilting. The value of this ratio might be, therefore, an index to compare the degree of the xerophytism of plants, the more xerophytic being a plant, the lower is the value.