An estimate of the amount of absorption may be obtained either in the field or in the control house by taking samples from the protected soil at different times. Since it is impossible to determine the weight of the area in which the roots lie, and since the soil water is often unequally distributed, this method can not yield exact results. An accurate method of measuring absorption under essentially normal conditions has been devised and tested in the control house. The essential feature of the process is the placing a plant in a soil containing a known quantity of water, and removing it after it has absorbed water from the soil for a certain period. In carrying out the experiment, a soil consisting of two parts of sod and one of sand was used, since the aeration is more perfect and the particles are more easily removed from the roots. The soil was completely dried out in a water bath and then placed in a five-inch battery jar. The latter, together with the rubber cloth used later to prevent evaporation, was weighed to the decigram. A weighed quantity of water was added, and the whole again weighed as a check. Two plants of _Helianthus annuus_ were taken from the pots in which they had grown, and the soil was carefully washed from the roots. Each plant was weighed with its roots in a dish of water to prevent wilting, and then carefully potted, one in each battery jar. A thistle tube was placed in the soil of each jar to facilitate aeration, as well as the addition of weighed amounts of water, when necessary, and the rubber cloth attached in the usual manner to prevent evaporation. The entire outfit was weighed again, and the weighing repeated at 8:00 A.M. and 5:00 P.M. for five days, in order to determine the amount of transpiration and its relation to the water absorbed. The plants were kept in diffuse light to prevent excessive water loss while the roots were becoming established. At the close of the experiment, the jar and its contents were weighed finally. The plants were removed and weighed, the soil particles being shaken from the roots into the jar, which was also weighed. The results obtained were as follows: ══╤═════════╤═══════════════════╤════════╤════════╤════════╤══════════ │ Wt. of │Wt. of pot and wet │ Total │_H_{2}O_│_H_{2}O_│ _H_{2}O_ │ pot and │ soil │_H_{2}O_│ left │absorbed│transpired │dry soil │ │ │ │ │ ──┼─────────┼─────────┬─────────┼────────┼────────┼────────┼────────── │ │ I │ II │ │ │ │ I│1846.0 g.│2218.0 g.│2174.3 g.│372.0 g.│328.3 g.│ 43.7 g.│ 43.7 g. II│1886.7 g.│2253.2 g.│2221.6 g.│366.5 g.│334.9 g.│ 31.6 g.│ 31.6 g. ──┴─────────┴─────────┴─────────┴────────┴────────┴────────┴──────────