332 PHYSIOLOGY OF THE FUNGI 



evident that a proper balance between the amounts of vitamins and 

 supply of nutrients is necessary for maximum production of asexual 

 spores. The effects of the concentrations of thiamine and glucose upon 

 the production of conidial heads by Choanephora cucurhitarum are illus- 

 trated in Table 58. On the other hand, we have observed that an excess 

 of certain vitamins may cause a decrease in sporulation of some fungi. 



OTHER FACTORS 



Method of inoculation. The method of inoculation and the type of 

 inoculum used are often important factors affecting sporulation in cul- 

 ture. Some fungi sporulate more quickly, and often more abundantly, 

 on agar when the medium is flooded with a spore suspension than when 

 the inoculum is placed at only one point. This is particularly applicable 

 to certain pycnidium- or acervulus-producing fungi, which usually pro- 

 duce abundant mycelium before fruiting. 



It is possible that the spores of certain fungi carry over sporulation- 

 inducing substances to the next generation. The production of conidia 

 of CoUctotrichum lindeviuthianum was greater on agar media inoculated 

 at one point with spores than when bits of mycelium were used as inocu- 

 lum (Mathur et at., 1950). 



Method of sterilizing media. The most common method of sterilizing 

 culture media is the use of steam pressure in an autoclave. The standard 

 time is usually 15 to 20 min. at 15 lb. pressure. This temperature is 

 known to cause a breakdown of certain sugars, with an accompanying 

 change in acidity of the medium. When natural media are used, other 

 chemical changes occur, which may or may not be beneficial to reproduc- 

 tion of the fungi. Shanor (1936) reported that fruiting structures of 

 Cordyceps militaris were not formed when autoclaved insects were inocu- 

 lated, whereas the fungus produced stromata and perithecia when living 

 pupae were inoculated. A new approach to the problem of sterilization is 

 suggested by Hansen and Snyder (1947), who propose the use of propylene 

 oxide. This method has great possibilities but has not been used exten- 

 sively enough to determine all its virtues and limitations. 



Influence of the host. Numerous parasitic fungi which have been 

 grown on artificial media have not been induced to form the sexual repro- 

 ductive stages under any conditions in culture. Some of these will 

 produce the reproductive stages when grown on their respective hosts. 

 For instance, most smuts will produce mycelium in culture, but few have 

 produced teliospores (''chlamydospores") under these conditions. Claviceps 

 has never been induced to form sclerotia (which necessarily precede the 

 perfect stage) in artificial culture. Other fungi seem to lose their ability 

 to sporulate profusely in culture but may regain that ability when grown 

 on the appropriate host. It may be pointed out that many of the fungi 



