Hoagland 



40 — 



Plant Nutrition 



These complicated interrelations of auxin and zinc 

 in terms of elongation by no means explain all the 

 responses of the plant to zinc deficiency. For example, 

 Reed and Dufrenoy (1942) have shown that pro- 

 found cytological changes occur in green leaf cells 

 and in growing points as an end result of zinc de- 

 ficiency. In the leaves of certain species of fruit trees 

 the presence or the form of phenolic substances in cell 



Textfigure 6. — Continued from textfig. 

 5. (From Skoog, 1940). 



vacuoles was a general character accompanying the 

 disease, although these effects are not necessarily spe- 

 cific to zinc deficiency. Destruction of chloroplasts or 

 inhibition of their formation is generally noted in ex- 

 amination of leaf cells of zinc deficient plants. Lytic 

 factors may destroy most of the cell contents in ex- 

 tensive areas of tissue. {See plate 15). 



Protein synthesis in the plant is markedly influ- 

 enced through some direct or indirect action of zinc, 

 for which view I may cite briefly some recent experi- 

 ments conducted in our laboratory by Bean (1942). 



