232 



MODIFICATION OF THE SOIL POPULATION 



of suKur for the purpose of making the soil more acid becomes 

 essential in a system of soil management devised to control such 

 plant diseases as potato scab, sweet potato pox, and potato wart 

 (Fig. 83). Other instances where soil inoculation appears to be 

 quite beneficial have been observed; the inoculation of seed beds 



Fig. 83. — Influence of sulfur and inoculation on potato scab. Upper series, 



tubers from check plot. Left to right: salable scabby, unsalable scabby. 



Lower series, tubers from plot treated with 600 pounds of inoculated sulfur. 



Left to right: clean, salable scabby, unsalable scabby (from Martin). 



of forest seedlings with mycorrhiza fungi and the inoculation of 

 soils with certain cannibalistic nematodes which are capable of 

 destroying the nematodes which cause certain galls on plants 

 have proved useful. Such treatments have value only in very 

 specific cases, and their use is still of uncertain practical appli- 

 cation. 



