38 



PHYSIOLOGY OF THE FUNGI 



nutrients which is most favorable for growth may be poor in other 

 respects, e.g., for reproduction. The concentration may be varied in two 

 ways: (1) by dihiting the entire medium, whereby the ratios among the 

 constituents remain unchanged, and (2) by varying the concentration of 

 one constituent. These methods are not equivalent and yield different 

 results. 



When an entire medium is diluted, it might be expected that the de- 

 crease in amount of mycelium produced would be directly proportional 

 to the amount of dilution. Such is not always the case. When Chae- 

 tomium convolutum was grown in full-strength medium and in medium 

 diluted to one-fourth and one-sixteenth full strength, the maximum 

 weights of mycelium produced were 220, 75, and 22 mg., respectively 

 (Lilly and Barnett, 1949). C convolutum grew most efficiently in the 

 most dilute medium. This principle appears to be generally valid and is 

 also illustrated by Ceratostomella fimbriata (Table 57) . 



Table 8. 



The Effect of Different Volumes of Medium upon the Rate and 

 Maximum Amount of Growth of Sordaria fimicola 

 Dry weight of mycelium in milligrams. 



When the concentration of one constituent in the medium is changed, 

 over a certain range, the amount of growth will be proportional to the 

 concentration. Above a certain concentration there will be no further 

 increase in the amount of growth. This is due to the limiting concentra- 

 tion of some other constituent in the medium. This is the principle upon 

 which fungi are used in vitamin and other assays (Chap. 10). 



The maximum weight of mycelium which is obtained from a given vol- 

 ume of medium depends upon the type and size of the culture vessels used. 

 The rate of growth is also affected. These results appear to be due 

 mainly to differences in aeration, and perhaps to a lesser degree to diffu- 

 sion. The effect of depth of medium on rate and amount of growth in non- 

 agitated cultures may be demonstrated by using a constant volume of 

 medium in different-sized flasks, or by varying the volume of medium in 

 flasks of the same size. Data illustrating this latter condition are pre- 

 sented in Table 8. The slow initial rate of growth when the mycelium is 



