224 ^' R- Hoagland 



was clearly shown that ability to absorb solutes against concen- 

 tration gradients (accumulation) is dependent upon a state o£ 

 intense cell metabolism, which is reflected in the processes o£ 

 aerobic respiration. This does not mean, however, that carbon 

 dioxide production is a direct measure o£ the power of accumu- 

 lation; in fact, there is reason to suppose that certain other meta- 

 bolic transformations not readily measurable, but reflected by 

 the ability of cells to grow and divide (according to Berry and 

 Steward'"), may be more directly related than respiration, as 

 determined by carbon dioxide production, to the process of 

 absorption and accumulation of solutes. In any event, a suitable 

 supply of oxygen is requisite to those activities which must be 

 set in action before the cell can remove solutes from a dilute 

 outer solution and transfer them to an inner solution of higher 

 concentration. Furthermore, these metabolic processes must pro- 

 ceed at a certain minimal rate in order that the cell may retain 

 solutes already accumulated in the sap. The applicability of these 

 general principles to growth of plants in the soil has been demon- 

 strated by extensive studies conducted in this laboratory in recent 

 years on the nature of absorption and accumulation of mineral 

 solutes by root cells. A new approach is oflFered to many prob- 

 lems of availability of nutrient elements. 



Oxygen Requirement for Accumulation 

 OF Solutes by Root Cells 



One out of many experiments will illustrate the indispensable 

 requirement of oxygen for the process of accumulation of 

 mineral solutes by root cells. In this experiment barley plants 

 were grown in culture solution for three weeks and then the 

 entire root systems were excised, a very large number of uniform 

 plants being used. One set of excised roots was placed in an 



