1 . Cultivation 

 and 

 Growth 



Xhe precise definition of growth in fungi depends on 

 the method of measurement used. Most methods determine, directly 

 or indirectly, the increase in mass of an inoculum after a known in- 

 cubation in a complete medium. Increase in mass or in number of 

 cells may therefore be used as an operational definition of growth. 



In considering cultivation and growth we shall first concern ourselves 

 with methods of cultivation and preservation of fungi, the dynamics 

 of growth, dimorphism, and the measurement of growth. Then we 

 turn to external factors — temperature, hydrogen-ion concentration, 

 oxygen, carbon dioxide, and water — as they affect growth. The same 

 external conditions also influence spore germination (Chapter 12); 

 radiant energy effects are taken up in Chapter 13. 



1. METHODS OF CULTIVATION 



Cultures of fungi are usually maintained on conventional agar slants, 

 and the agar petri dish has been employed in experimental work. Most 

 quantitative studies, however, require a liquid medium which may be 

 either surface (still) or submerged (aerated) culture. 



The general technique of surface culture is too well known to require 

 description here. It is not always realized that normal aerobic growth 

 can be obtained only if the inoculum floats on the surface of the 

 liquid. Many spores float naturally; for those that do not, use of a 

 bran-cultivated inoculum (206) or inclusion of a small amount of agar, 



1 



