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



99 



roots per plant, and the 0.58 atmospheres concentration a yield of 0.66 ± ' 

 o.oS gm. of tops and 0.24 gm. of roots. Between these figures there is no 

 significant difference, although in water cultures, series i and series 4, 

 similar solutions gave distinctly different yields. To verify these results 

 finally it will be necessary to repeat the experiment at a more favorable 

 season of the year; but we may reasonably conclude, taking all the 

 experiments into consideration, that with a solution of the general 

 composition described above the optimum concentration for the barley 

 plant — defined as the least concentration producing a yield equal to any 

 higher concentration — is not higher than 0.60 to 0.90 atmospheres 

 and may be less than o.io atmospheres. This point is to be considered 

 more critically in the final discussion. 



In one of the preceding experiments reference was made to the obser- 

 vation that under certain conditions electrolytes might leave the plant 

 and return to the solution. In order to gain some additional insight into 

 this process, a number of plants which had grown for 6 weeks in favorable 

 nutrient solutions were transferred to various very dilute nutrient 

 solutions after washing the roots thoroughly in distilled water. The 

 results are presented in Table XI, in which comparisons are made 

 between the resistances of original solutions and the same solutions 

 after contact with the plant. 



Table XI. — Absorption by plants from dilute solutions 



1 Solutions changed. 



In the two most dilute solutions the electrolyte concentration was 

 increased, and from the three higher concentrations absorption took 

 place. Later absorption occurred from all solutions, so that in several 

 cases the resistance of the solutions became about the same as that of the 

 distilled water used. Subsequently there was a further excretion of 

 electrolytes from the plant. True and Bartlett (49, 50, 5 1 ) have described 

 phenomena similar to these, working with partial nutrient solutions in 

 very great dilution. 



True {48) has also pointed out that distilled water may be injurious 

 because of the elements leached out from the plant. In order to ascertain 

 which elements would leave the plant we have transferred a number of 

 122504°— 19 4 



