Hoagland — 58 — Plant Nutrition 



CO2 concentration is required to depress greatly the 

 process of salt accumulation. A very small oxygen 

 tension in the gas stream will induce some salt ac- 

 cumulation to occur. In our recent experiments, how- 

 ever, in which all feasible precautions were taken to 

 exclude oxygen, we have never observed any certainly 

 significant movement of an ion into the plant against 

 a gradient of concentration, as judged by analysis of 

 expressed sap. 



10 20 30 40 50 60 70 80 90 100 

 PERCENT OXYGEN IN GAS MIXTURE 



Textfigure 11. — Effects of oxygen in the gas stream sup- 

 plied to excised barley roots on accumulation of various ions 

 and on sugar utilization. (From Hoagland and Broyer, 1936). 



Since metabolic activities dependent on or asso- 

 ciated with aerobic respiration govern salt accumula- 

 tion in the roots, it is to be expected that the tem- 

 perature coefficient of the process should be high 

 within certain biological temperature ranges. The ex- 

 pectation is borne out by the experimental evidence 

 on this point. The temperature effect may not be re- 

 vealed, of course, unless experiments are made on 

 roots with a high salt absorbing capacity and in the 



