Hoagland — 170 — Plant Nutrition 



ultimately necessary for every kind of synthesis or 

 metabolism in the plant. The question at issue is how 

 direct a role does it play in any given physiological 

 process. 



One way to approach this problem is to study plants 

 subjected to potassium deficiency for limited periods 

 of time and observe some of the effects on organic 

 constituents of the plant. I should like to cite for 

 illustration a series of experiments in which I co- 

 operated with Professor A. R. Davis. These experi- 

 ments were carried out with young wheat plants grown 

 in temperature controlled chambers under known arti- 

 ficial illumination. Some sets of plants were furnished 

 nutrient solutions with a supply of potassium inad- 

 equate to produce the full growth of the plants that 

 was possible under the given climatic environment, 

 but not so inadequate as to produce a marked degree 

 of potassium starvation. For analysis, the shoots of 

 the plants were divided into upper and lower portions, 

 also the roots. 



The total sugar concentrations of the potassium 

 deficient plants were decidedly greater than those of 

 the plants receiving the larger supply of potassium. 

 In one experiment at least, the total amount of sugar 

 per unit number of plants was approximately the same 

 for the low and high potassium plants, despite the 

 smaller size of the deficient plants. It did not appear 

 that over the experimental period the potassium de- 

 ficient plants were retarded in their growth directly 

 by lack of carbohydrate synthesis or translocation. 

 Also, some evidence from these and similar experi- 

 ments, and a large amount of evidence by other work- 

 ers, indicates that soluble organic nitrogen is often 

 higher in concentration in low potassium plants than 

 in high potassium plants. 



A suggestion is derived that potassium is essential 

 for some step in protein synthesis. In line with this 

 concept are the data by Steward and his collaborators 

 on biochemical changes occurring during the absorp- 



