T. C. Btoyer 225 



in several studies (?/, 45/ compare 9/). Data from one such experiment 

 are reproduced in Table VII (?/). Here, the pH values of exudates 

 from decapitated plants show remarkable constancy even though the 

 hydrogen ion concentration of the medium bathing the roots varied 

 over a wide range. The accumulation of inorganic solute which was 

 indicated by potassium and bromide concentrations in the exudates 

 was not appreciably different. This point will be referred to later in 

 another connection. 



TABLE VII 



pH Effects on Concentration of Potassium and Bromine in Exudate from 



Barley Seedlings 



pH External Solution pH Exudate Concentration in Exudate 



Initial Final K Br 



Note: Initial concentration in exudate — K = 12.5; initial concentration external solution = 

 5; exudate collected during period of 6 hours. 



BIOCHEMICAL ASPECTS — ENERGETICS AND MECHANISM 



Growth and metabolic level 



Steward (75, j6) has drawn attention to a possible correlation be- 

 tween salt accumulation by cells and the growth and metabolism 

 thereof. His chart of the relative rates of net movement of inorganic 

 solute into various types of plant cells and tissues is reproduced as 

 Figure 21. The favorable situation of roots may be seen, showing 

 marked salt accumulation under favorable external and internal con- 

 ditions. Here, also, are summarized the effects of previous history, 

 particularly physiological preconditioning on further accumulation of 

 salt. Steward also stresses renewal or continuance of growth as requisite 

 for further primary or active absorption (compare Lundegardh, 46). 

 In certain of his own studies with storage tissues, he has obtained data 

 which he feels suggest a correlation between protein formation and 



