INFLUENCE OF TEMPERATURE 189 



the stage of development ; in the earliest phase, when the 

 spores are germinating, Q 10 = 2-8 ; when the mycelium is 

 established and growing well, O 10 = 1-6. 



Balls * measured the growth in the length of the hyphae 

 of the fungus causing " sore skin " on the cotton plant. The 

 growth rate at different temperatures is what might be ex- 

 pected from van't Hoff's law ; but at higher temperatures, 

 38 C, there is a decrease in growth followed by complete 

 cessation probably due to the accumulation within the cell of 

 certain products of catabolism ; these deleterious substances 

 presumably are formed at lower temperatures but at a much 

 slower rate ; they diffuse out into the surrounding medium, 

 especially at higher temperatures, possibly on account of 

 alterations in the permeability of the protoplasm at these 

 higher temperatures. j In higher plants, the outward dif- 

 fusion of these harmful bodies, provided they be formed, 

 must be slower on account of the more massive nature of the 

 structures, or they are oxidized within the tissues themselves. 

 As Balls points out, since the conditions in which this 

 decomposition takes place must be fairly uniform in a higher 

 plant, growth optima are shown which are the expressions 

 of the internal struggle between the increasing rapidity of 

 chemical change with the rise in temperature and the inhibitory 

 action of the accumulating products of catabolism. 



Brown { in his study of the growth of various fungi, as 

 indicated by the increase in the diameter of the colonies growing 

 in the culture media and by the estimation of the amount of 

 rotted portions of fruits artificially infected, paid particular 

 attention to the relation between temperature and carbon 

 dioxide concentration, which factors are of great economic 

 significance in the storage of fruit. His main conclusion is 

 that the relative retarding effect of a given concentration of 

 carbon dioxide on the growth of fungi is greater at a low than 

 at a high temperature, which can only partly be explained by 

 the fact that this gas is more soluble in water at a low than 



* Balls : " Ann. Bot.," 1908, 22, 557. 



t See Eckerson : " Bot. Gaz.," 1914. 5 8 > 2 54- 



I Brown : " Ann. Bot.," 1922, 36, 257. 



