34 Killing of Botrytis Spores by Phenol 



to the normal curv^e, it gives an adequate and satisfactory explanation 

 of the sigmoid curve. 



If, however, we examine more closely the curves obtained with 0-5, 

 0-6 and 0-7 per cent, phenol, it becomes apparent that their shape, though 

 still sigmoid in character, differs from that of the 0-4 per cent, curve, 

 the difference being progressively more marked as the strength of phenol 

 is increased. All the experiments recorded in Tables I — IV were done 

 with adult spores in approximately equal numbers and at nearly the 

 same temperatures. They may fairly be compared ; and in the following 

 table (V) the results of these and other^ similar experiments done with 

 each strength of phenol are brought together. The curves were drawn 

 for each experiment, and the times required to kill 25, 50 and 75 per 

 cent, of the spores read off, and from these readings the mean times 

 for each strength of phenol obtained. 



Table V. Times in minutes taken to kill 25, 50 and 75 per cent, spores 

 by 0-4, 0-5, 0-6 and 0-7 per cent, phenol. In brackets are given 

 the figures for each wath the 0-7 per cent, times taken as unity. 

 Phenol 



It will be seen that the times required fall rapidly as the strength of 

 the phenol is increased — e.g. while 90 minutes are required with 0-4 per 

 cent, to kill 25 of each 100 spores, with 0-7 per cent, only 2-6 minutes 

 are necessary. But it is also apparent that the ratios of the times 

 required vary greatly, if we compare the 25 per cent, with the 50 and 

 75 per cent, columns. It takes 34 times as long for 0-4 per cent, phenol 

 to kill 25 per cent, of the spores as for 0-7 per cent, to kill the same 

 number: but it takes only 19 times as long for 0-4 per cent, to kill 75 per 

 cent, as for 0-7 per cent. With the strong poison the time of killing is 

 much more reduced in the early part of the process than it is in the later 

 stages. The effect of increasing the quantity of phenol is to accelerate 

 the kilhng much more markedly in the early part of the curve — i.e. 

 increasing the phenol tends to remove the slow stage at the beginning 

 of the curve and to reduce the sigmoid character: the curve tends more 

 and more to approach the logarithmic type as the phenol is more and 

 more raised. 



1 The cost of printing at jiresent prevents these being given in full. 



