SPORULATION 



307 



studied during the past 50 years, and some new factors have been brought 

 to light. It would not be surprising if some modifications in these con- 

 clusions would be necessaiy in the light of 50 years of research. We shall 

 find, however, that, in the main, many of these "laws" are still valid. 



ENVIRONMENTAL FACTORS 



Temperature. Temperature was recognized by Bisby (1943) as an 

 important natural factor governing the geographical distribution of the 

 fungi. The temperature must be favorable not only for growth but also 

 for the production and germination of the spores, if the fungus is to 

 survive. Certain fungi are limited by high temperatures. Among these 

 are Plasmodiophora brassicae, Colletotrichum lindemuthianum, Urocystis 

 cepulae, and certain Phycomycetes. On the other hand, certain genera 

 of the Gasteromycetes, such as Podaxis, Battarrea, Chlamydopus, and 

 Phellorina, are confined to the hot arid regions of southwestern United 

 States, northern Africa, central Australia, and western India. Between 

 these extremes we may observe many examples where seasonal tempera- 

 ture limits or favors reproduction. 



Klebs (1900) pointed out that the temperature range which allowed 

 sporulation was more narrow than the range for growth. In general, the 

 temperature limits for sexual reproduction are narrower than the limits 

 for asexual reproduction. Some of Klebs's data are presented in 

 Table 53. 



Table 53. Minimum and Maximum Temperatures (in Degrees Centigrade) for 



Growth axd Sporulation of Various Fungi 



(Klebs, Jahrb. iriss. Botan. 35, 1900.) 



Fungus 



Aspergillus repens. . . 

 Sporidinia grandis. . . 

 Piloholus rnicrosporus 

 Saprolegnia mixta. . . . 



Growth 



Min. 



7-8 

 1-2 

 2-4 

 0-1 



Max. 



37-38 

 31-32 

 33-34 

 36-37 



Asexual spores 



Min. 



8-9 



5-6? 



10-12 



1-2 



Max. 



35-36 

 29-30 

 28-30 

 32-33 



Sexual spores 



Min. 



5-6 



1-2 



Max. 



33-34 



27-28 



26-27 



It will be noted that the upper temperature which allowed the produc- 

 tion of oospores by Saprolegnia mixta is a full 10°C. less than the upper 

 temperature limit at which growth took place. Coons (1916) found the 

 temperature limits for the growth of Plenodomus fuscomacidans to be 

 to 33°C., while pycnidia formed between 6 and 30°C. Perithecia failed 

 to form in cultures of Ceratostomella fimbriata kept at 18°C. for 60 days 

 (Barnett and Lilly, 1947a). Cultures of this fungus on the same medium 



