22 



THE COTTON PLANT IN EGYPT CHAP. 



25 C. 



d& 



0-060 



5 0-030 



10 20 30 40 



Minutes 



Maximum rate - 0-0055 mm. per minute 



FIG. 31. GROWTH AND TEMPERATURE OF A FUNGUS. 



Hypha of "Sore-shin." 



slow, we find that growth stops even in a culture kept 

 constantly at 20 C., if kept long enough. Such cessation 

 of growth is not necessarily due to exhaustion of food 

 from the culture, for all the food-ingredients may still be 

 present. Further, it takes place, for any given temperature, 

 after a lapse of time which is directly proportional to the 

 volume of the culture media. Lastly, such " stale 

 cultures " will resume their growth if they are diluted with 

 pure water. 



Plainly, then, the staling of cultures is due to excretion 



