Hoagland 



— 8 



Plant Nutrition 



relations to the solid phase of the soil were different 

 and also their relations to the selective absorption of 

 ions by living root cells. Some ions fluctuated in con- 

 centration more widely than others. 



The phosphate ion was present usually in very 

 low concentrations. Potassium fell in an intermediate 

 position. The total amounts of phosphate ions present 



Sotutioms displaced from cropped (A) soils at beginning and at the end of the growing scasMt 

 {19Z3) and at the beginning of the next grounng season {1924) 



Table 1. — Composition of solutions displaced from 

 cropped soils at beginning and end of growing season 

 and at beginning of next growing season. (From J. S. 

 BuRD and J. C. Martin, 1924). 



in solution in the whole mass of the soil, at the be- 

 ginning of the season, were far short of accounting 

 for the amounts absorbed by the crop during its growth 

 period. On the assumption that the soil solution was 

 the immediate source of all the nutrients absorbed by 

 the plant,* it was necessary to conclude that as plants 

 grew and absorbed phosphate, this ion had to be re- 



*An additional mechanism will be presented at a later time. 



