Oct. IS, 1919 Relation of Nutrient Medium to Plant Absorption 



89 



ferred to solutions of the four different concentrations previously men- 

 tioned. The absorption and transpiration were then determined for a 

 period of two days, after which the plants were cut and the dry weight 

 determined. 



Table VI. — Transpiration and absorption by uniform plants 

 WATER CULTURES, SERIES I 



These results are interpreted to mean that the concentration of the 

 solution has a marked effect on absorption and transpiration. Almost 

 double the quantity of water per gram of dry weight is transpired by 

 the plants in the solution of lowest concentration as compared with 

 the quantity transpired by those in the highest concentration. • In the 

 solution of lowest concentration there was possibly a slight excretion 

 of electrolytes from the plant. In the other solutions absorption took 

 place in the order of increasing concentrations. 



It has sometimes been assumed that transpiration may be regarded 

 as proportional to the dry weight of the plant and that the effect of vari- 

 ous solutions may be reflected in the transpiration. Livingston {24) and 

 Whitney and Cameron {55) have tended toward this view ; on the other 

 hand Bouyoucos (2) has found that the concentration of the nutrient 

 solution has a decided influence on transpiration, the higher concentra- 

 tions diminishing water loss, either because of the difficulty experienced 

 by the plant in absorbing water from a solution of higher osmotic pres- 

 sure or because the increased osmotic pressure of the cell sap decreased 

 the vapor tension and so reduced transpiration. Our experiments uphold 

 the view that solutions of increased concentration have the effect of re- 

 ducing transpiration. Since plants of uniform development and ap- 

 proximately equal leaf surface display widely different transpiration 

 rates with solutions of different concentrations, it does not appear that 

 transpiration is necessarily an accurate criterion of growth. There is, 

 in fact, a preponderance of evidence to show that transpiration per unit 

 of dry weight increases with decreasing concentration. Kiesselbach 

 {21) and Khankhoje (20) reached this conclusion as a result of sand- 

 culture studies, while Preul {35) and Kiesselbach found that the water 

 requirement per unit of dry weight is less on a poor soil. Widtsoe (54) 

 says that fallowing and fertilization decreased the water requirement. 



