SPORULATION 319 



instance, it was possible to trace the connection between temperature and 

 the composition of the medium to a specific factor, i.e., acidity 



Perithecia were not formed by Sordaria fimicola until the pH of the 

 culture medium was 6.5 or greater (Lilly and Barnett, 1947). While 

 acidity of the medium was not the only controlling factor affecting the 

 formation of perithecia by S. fimicola, perithecia never formed when the 

 pH was less than 6.5, however favorable the other external conditions 

 were. 



OTHER PHYSICAL FACTORS 



It has frequently been observed that many species of fungi fruit more 

 readily when grown upon a solid or semisolid substratum than they do in 

 liquid media. Leonian (1924) reported that only 6 out of 20 species 

 studied formed pycnidia as readily in liquid medium as on solid medium. 

 He concluded that the beneficial effect of solid media was due to better 

 aeration and free transpiration. 



The favorable effect of ozone upon the formation of pycnidia and spores 

 of a limited number of fungi was recently reported by Richards (1949). 

 The production of viable conidia of three species of Alternaria was greatly 

 increased on exposure to ozone. Although conidium formation of 

 Mycosphaerella citrullina was increased by exposure to ozone, the spores 

 formed did not germinate. 



The transformation and elongation of basidia of certain Polyporaceae 

 in nature and under controlled conditions has been correlated with high 

 humidity by Bose (1943). It seems likely that the humidity of the 

 atmosphere may have a greater influence upon conidium formation in the 

 aerial fungi than is generally supposed. In Rhizopus, for instance, much 

 more liquid moves upward through the sporangiophore than can be con- 

 tained within the sporangium. A high percentage of this water must be 

 transpired in order to condense the protoplasm and food materials stored 

 in the spores. A change in relative humidity must affect the rate of 

 transpiration. On the other hand, Ternetz (1900) found that a humidity 

 of 98 per cent or higher was necessary for fruit-body production by 

 Ascophanus carneus. Actually, we know little about the influence of 

 humidity, and much more information is needed on this subject. 



Emerson and Cantino (1948) showed that the presence of high concen- 

 trations of carbon dioxide favored the production of resistant sporangia 

 by Blastocladia pringsheimii. 



Mutilation of the mycelium, which would cause the death and release 

 of cellular constituents, has been used to stimulate sporulation (see Rands, 

 1917; Kunkel, 1918; and McCallan and Chan, 1944). Scraping of the 

 mycelium of Alternaria solani followed by a brief exposure to ultraviolet 

 rays was used successfully by McCallan and Chan (Fig. 63). 



