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CIRCULAR NO. 127, BUREAU OF PLANT INDUSTRY. 



ing this treatment the specimens were placed in moist chambers 

 under conditions favorable for the fungus to fruit. Iji every case 

 viable spores were produced from 2 to 12 days after treatment. The 

 germinating capacity of the spores was determined by placing them 

 in water for 24 hours. In every case the spores germinated. 



As shown in Table I, neither corrosive subhmate nor formalin 

 used twice as strong as in common practice for a period of five hours 

 killed the fungus. 



Table I. — Effect of formalin and corrosive sublimate on silver scinf. 



These data suggest that the ordinary formalin and corrosive- 

 sublimate methods in vogue for controllmg Oospora scab do not kill 

 Spondylocladium. This is not surprising in view of the fact that 

 the fungus produces numerous sclerotia and penetrates all parts of 

 the periderm and in severe cases even extends into the parenchyma. 

 Johnson used an 0.8 per cent solution of formalin and succeeded m 

 preventing the reappearance of silver scurf. An 0.8 per cent solu- 

 tion of formalin is twice as strong as that commonly used in this 

 country for Oospora scab. In the test on January 30, 1913, recorded 

 in Table I, a double strength of corrosive sublimate (about 4 ounces 

 to 15 gallons of water) killed the tubers, but the fungus developed 

 viable spores after 7 days. On March 20, infected tubers were 

 soaked 19 hours in an 0.8 per cent formalin solution and immediately 

 placed in a moist chamber. The fungus produced viable spores 

 after 10 days. It should also be noted that many of the eyes of 

 the tubers w^ere killed by this treatment. Neitlier does dr}' heat at 

 50° C. for 5 hours kill the fungus. This was learned in connection 

 \\dth numerous experiments planned to determine the effect of dry 



[Clr. 127] 



