226 



D. R. Hoagland 



D INITIAL CONC. IN SAP 



ABSORPTION WITH 



ABSORPTION WITH AIR 



O 

 X 



o 



X 

 S 



ft. 



>■ 



O 



3 

 O 

 Z 

 O 



u 



Fig, I. Effect of aeration on accumulation of salt by excised roots of barley 

 plants. 



Each set of root systems represents i68 plants previously grown in a complete 

 culture solution from May 31 to June 26. Absorption period, lo hours; tempera- 

 ture of solution, 24° C. 



^ . , 1 • (KBr .0075 M) 



Experimental solution: .' .^^^ . -^A 3000 cc. 



^ |Ca(N03)2 .0025 M^ 



pH of culture: initial, 6.0; final, air 5.8; N2, 6.3. 



During the absorption period, a rapid stream of air was passed through one 

 solution and purified nitrogen gas through the other. The nitrogen gas, however, 

 retained traces of oxygen. Some oxygen was also present in the tissue and solution 

 at the beginning of the absorption period. 



It should be noted that much of the nitrate absorbed was reduced, and that 

 potassium absorbed in association with nitrate remained in the sap in equilibrium 

 with organic acid anion formed in the course of metabolism. 



Numerous consequences arise from the principle that absorp- 

 tion and accumulation o£ mineral elements are dependent on 

 protoplasmic activities. In the first place, the oxygen requirement 

 of root cells and the oxygen-supplying power o£ the soil assume 

 a new and specific significance. No matter what the concentra- 

 tion of solutes in the soil solution may be, these solutes are not 



