! 



ditions oflthe fungus as the culture becomes older. -. re- 

 lation of growth rate to ace of culti may "be studied by ref- 

 erence either to the original mean 24-hour rat^s for the d : '- 

 ferent consecutive observation periods and for tbe four fungj 



(tables HI- YD t or to the derived rate* riven in tables 

 IX - XII or by reference to graphs of figures 2-5 and fig- 

 ures 11 - 13. 



Inspection of tbe tables IX - XII and graphs (figures 

 11 - 13) shows that the mean rate of enlargement alters with 

 the ape of tbe culture in three reneral ways. 1 - lower 

 temperatures the rate increases throughout the culture period, 

 the rate of increase being generally greatest for the first two 

 days and much more gradual afterwards. (2) For a few high- 

 er temperatures the rate first increases and then decreases, 

 sometimes remaining constant for two 24-hour peri cds or long- 

 er. (3) For the highest temperatures the rate decreases 

 throughout the culture period, this decrease soon bringing the 

 value to zero for the yery highest temperatures studied. 



Cha rges in Maximum and Optimum Temperature with Lapse 

 of Time • It is a common observation that at certain biph 

 temperatures near the maximum temperature, the rate of certain 

 processes diminish rapidly with time. As bar been pointed 

 an examination of the data of tables 21- 3Z£ figures 2-5 



and figures 11 - 13 show that at certain temperatures that 

 were below the maximum for the first observation period, the 

 rates fell off rapidly to zero with time in all -che fungi so 

 that the maximum temperature was definitely moved baclc at each 

 subsequent 24-hour period. 



In two of the fungi, Pythiacystis and Diplcdia, the 



66 



