42 Killing of Botrytis Spores by Phenol 



Table XIX. 12. 4. 20. 6 day spores. Phenol 0-7 per cent. 25-2' 



Time in 60,000 in Value 



With 9 day spores the sigmoid character is clear, more marked with 

 240,000 than with 30,000 spores to the 1 c.c. With 7 day spores, however, 

 the character is altered. There is no longer perceptible to the eye an 

 initial period of increasing rate and the curve falls steeply from the 

 start and then slows off as before. It approaches much more closely 

 to the logarithmic type than any of the preceding curves {v. Fig. 5). 

 In the table (XVIII) is added the values of k on the assumption that 

 the process follows the unimolecular formula k ^ l/t log a/a — x, where 

 a is the original number of germinable spores and x the number dead 

 at time t. The constancy of k is not so good as one would hope for, even 

 in this type of work, and rises definitely towards the end. With 6 day 

 spores, however (the youngest spores which it was found practicable 

 to use), the value of k is as constant as one can reasonably expect, at 

 least until only about 4 per cent, of the spores are still surviving 

 {v. Table XIX). In Fig. 6 the curve is drawn from the formula with 

 k = 0*226, and the observed points fall very closely on the curve. In 

 Fig. 6 also the logarithms of the observed values are plotted against 

 time, and the points from 100 per cent, to under 10 per cent, fall very 

 fairly on a straight Hne. 



With sufficiently young spores, then, the curve is of the logarithmic 

 type, and the sigmoid character has disappeared. It was of interest to 

 determine whether with a low strength of phenol it would be possible 

 to restore the sigmoid shape, when using spores which gave the log- 

 arithmic type with the higher strength. An experiment was accordingly 

 performed with G day spores and two strengths of phenol. The same 

 suspension was used in both cases, one- half being exposed to 0-7 phenol. 



