274 Journal oj Agricultural Research voi. 45, No. 5 



The length of the incubation period in relation to the decreasing 

 number of spores used varied greatly with the different lots of spores, 

 even with the duplicate inoculations of each lot. Table 5 gives the 

 results of positive cultures obtained in relation to the period of incu- 

 bation and the dilution of the spores. The coefficient of correlation 

 {14, -p. 179) for the positive cultiu-es only, in relation to length of 

 incubation and dilution of spores, was found to be 0.3558 ±0.0440. 

 While this does not show a strong correlation, it indicates that with 

 the smaller numbers of spores there is a tendency for growth to take 

 place with longer periods of incubation. However, when the cases 

 of positive growth were correlated with the dilution and incubation 

 time on the basis of the percentage of positive cultures to negative 

 cultures for each observation period of incubation time, an insignifi- 

 cant negative correlation was obtained. Apparently there is a 

 variable uncontrollable factor present, more obvious when spores are 

 used from different lots of the organism, which makes it impossible 

 to correlate the other factors closely. However, the data summarized 

 in Table 6 indicate that, of the 120 cultvu-es made with seedings of 

 between 5,000,000,000 and 9,000,000 spores per seeding, 98.33 per 

 cent showed growth at the end of 10 days' incubation, while 100 

 per cent (120 cultures) showed growth after 30 days' incubation. 

 This is 56.87 per cent of the 211 total cultures showing growth 

 after 30 days. 



