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



87 



Table Y.— Effect of concentration on growth and transpiration 



WATER CULTURES, SERIES I 



A series of sand cultures was carried out to parallel the water cultures; 

 but since there was some indication that the paraffine seal had exer- 

 cised an inhibitive effect on the growth of the plants, these data are 

 omitted. The evidence obtained, however, led to the conclusion that 

 the transpiration per unit of dry weight was greater in the sand cultures 

 than in the water cultures. This is in accord with the findings of 

 Bouyoucos (2). 



The absorption studies were made by means of conductivity measure- 

 ments. In each case comparisons were made under identical conditions 

 between solutions before and after contact with the plant. The general 

 trend of absorption is expressed in a graph. The absorption has been 

 calculated in terms of parts per million of total electrolytes absorbed, 

 based on concentration of the original solution. 



The total absorption is evidently greater in the solutions of higher 

 concentration, but in the solution of highest concentration there were 

 two periods when an increase was noted in the concentration of the 

 solution after contact with the plant. It may be inferred that the plant 

 had absorbed in the preceding period such an excess of one or more ions 

 as to cause a temporary reversal of the absorption processes, with a re- 

 turn of ions to the solution. These fluctuations are undoubtedly related 

 in some way to the general light and temperature conditions affecting 

 growth. In later experiments carried on out of doors during the spring 

 and summer the absorption followed a more uniform course. In the 

 greenhouse experiment, light conditions were not favorable to a high 

 yield, and considerable fluctuations in temperature occurred. 



In almost all experiments designed to show the relation of the con- 

 centration of the solution to absorption and transpiration, the seed- 

 lings have been grown from the beginning in the solutions which it was 

 desired to investigate. Any nutritive deficiencies in the solution would 

 thus be reflected in the development of the plant, and the fundamental 

 relations would be obscured. It would seem that the problem might be 

 simplified by growing the plant in a favorable nutrient solution until it 

 had reached a stage of active absorption and then transferring it for a 



