Plate 13. — Corn plants glowing in a soil (subsoil) naturally 

 deficient in zinc supplying power for various tree species. 



In the greenhouse corn plants develop "white-bud" symijtoms. Soil 

 on left — no treatment: next, soil previously autoclaved ; soil auto- 

 claved and reinoculated with unsterilized soil; soil similarly treated 

 but to which zinc was applied. This experiment was frequently re- 

 peatable but did not always succeed. Uncontrolled inoculations could 

 not be avoided. The hypothesis is that the growth of certain kinds of 

 microorganisms may have interfered with the absorption of adequate 

 amounts of zinc by the corn plants, possibly through competition for 

 zinc. 



