Oct. 15, 1919 Relation of Nutrient Medium to Plant Absorption 



95 



solution of o.io atmospheres concentration (Pg 6.5), however, gives a 

 different type of curve. During the fourteenth to sixteenth weeks, elec- 

 trolytes instead of being absorbed were returned to the nutrient solution. 

 During the final week absorption was again resumed. 



These measurements are particularly interesting, since Burd (7) has 

 observed an analogous phenomenon in the absorption of barley plants 

 grown in soils. In this investigation plants were cut and analyzed at 

 various stages of growth in such a way that the total content of the im- 

 portant elements could be calculated on the basis of an average plant. 

 At a certain period in the growth cycle, which coincided approximately 

 with the period of lowest concentration in the soil solution, there was a 

 marked loss of K and N from the tops of the plants together with a small 

 loss of Ca, Mg, and PO4. After several weeks, Absorption, or at least a 

 return of elements to the tops of the plants, again took place. Although 

 in a soil experiment it is not possible to recover roots quantitatively, it 

 is thought probable that a considerable portion of the elements lost from 

 the tops returned to the soil. Certainly in the solution-culture experi- 

 ment, electrolyte concentration increased in the solution mentioned. 

 This did not occur, however, in those solutions in which the higher con- 

 centration was maintained nor in the solution of low concentration with 

 an acid reaction. The latter fact may receive a possible explanation in 

 some experiments dealing with the effect of hydrogen-ion concen- 

 tration, to be discussed later in the article. 



The plants grown in this series, as in series 2, remained green in the 

 higher concentration. The heads ripened, but a good deal of the grain 

 had a shrunken appearance. The yields in terms of air-dry weight are 

 as follows: 



"■ Based on lo plants. 



The dry weight of the straw is somewhat greater where a higher con- 

 centration of solution has been maintained, but the yield of heads is not 

 significantly different. 



WATER CULTURES, SERIES 4 



This series had for its object the comparison of yields in solutions of 

 various concentrations and the determination of the absorption of each 

 ion from the different solutions during a given period of time. One-liter 

 bottles were employed with 2 plants in each bottle. Solutions were 



