The expressed sap from barley plants grown in water, sand, and soil cultures under controlled conditions has been examined with the following results: 1. The osmotic pressures in the sand and water cultures are reflected in the cell sap of the tops and roots. 2. The electrical conductivity of the nutrient solution has a marked influence on the conductivity of the sap. This is as marked for the tops as for the roots. The conductivity of the plant sap is from 4 to 50 times greater than that of the nutrient solution. 3. The sap from the tops of all plants grown in sand and soil cultures or water cultures of different concentrations and reactions had almost the same PH value, approximately 6.0. 4. Samples of sap from plants grown on 6 different soils under the same climatic conditions were analyzed for important elements. In every case the concentration in the sap was found to be very much greater than in the soil solution. 5. The dynamic nature of the relation between the soil solution and the plant is empha...