22 



iment with practically the same negative result as shown in the pre- 

 ceding one. The results of the three foregoing experiments shown 

 in Diagrams I, II, and III, are conclusive enough to indicate what 

 might be expected from this method of treatment, and we therefore 

 turn our attention to the testing of larger plots in connection with 

 sterilization. 



Experiment 4 (Diagram IV) shows the results of covering the top 

 of the plots with i in. and i^ in. of sterilized soil, the number of 

 plants in the three plots being 418. The percentage of Drop plants 

 in the untreated soil was 26% ; that in the i^ in. sterilized (a) 3.6%; 

 while that in i in. sterilized is 3.8%, or in other words, there is 

 shown in this experiment a saving of about 85 % of Drop by the use 

 of I in. and i .^ in. of sterilized soil. 



We have previously alluded to the effects of desiccation upon the 

 germination of sclerotia, but at the time experiment 5 was made the 

 remarkable acceleration which is produced by this means in the 

 development of the sclerotia was not fully comprehended by us. 

 We endeavored to see what effect a long period of thorough drying 

 would have upon the Drop and consequently closed up the house 

 during the greater part of August, September and October, at which 

 time it was subjected to the intense rays of the sun which heated the 

 soil up to a temperature of 123° F. and the air thermometer regis- 

 tered 140° F. As the top layer of the soil became dry, a lower layer 

 to the depth of a foot was forked over two or three times, so that 







• — Drop ©— Rhizoctonia 



Diagram V. Showing the effects of soil desiccation upon the Drop. The soil was dried 

 from August to October. 



