CULTIVATION AND GROWTH 



Time 



Figure 3. Growth of and changes in the medium by Aspergillus oryzae. Redrawn 

 from Crewther and Lennox (62), by permission of the Australian Journal of Bio- 



logical Sciences. 



short time with no further change thereafter (151). Autolyzing myce- 

 lium of Penicillium griseojulvum undergoes an extensive breakdown of 

 chitin, carbohydrates, and protein, catalyzed by enzymes of the fungus 

 (275). Other autolytic products include ammonia (74, 80, 160), free 

 amino acids (71, 108), organic phosphorus compounds (200), and sul- 

 fur compounds (137, 245). 



Cells at the end of the growth phase appear vacuolate; younger 

 cells have a denser and more homogeneous protoplasm (49). Such old 

 cells, of course, are found even during the growth period in regions 

 remote from the growing hyphal tips. 



From the rather limited data available, the cessation of active 

 growth appears to be determined by either of two factors. In concen- 

 trated media, toxic metabolites can be shown to accumulate and these 

 materials, earlier called "staling substances," demonstrably retard 

 growth (27, 37, 236). Probably organic acids, in high-carbohydrate 



