SPORULATION 311 



Ascochyta nymphaeae, Cytosporella mendax, Endothia parasitica, Keller- 

 mania yuccagena, Naemosphaera sp., Plenodomus destruens, and Phoma 

 urens formed more pycnidia at 30°C. in the dark than in the light at room 

 temperature. The following fungi failed to fruit in the dark at 8°C. but 

 fruited at the same temperature in the presence of light: Hendersonia 

 sp., Melanconium hetulinum, Naemosphaera sp., Pestalotia guepinia, 

 Phoma urens, Phyllosticta opuntiae, Sphaerographium fraxini , and Sphaero- 

 nema pruinosum. Light favored pycnidial formation by Plenodomus 

 fuscomacidans (Coons, 191G). The above examples make it clear that 

 light and temperature may serve as interchangeable stimuli to sporulation 

 in some, but not all, instances. Since the response (sporulation) is the 

 same whether light or temperature is the stimulus, this means that these 

 stimuli in some way brought about the same or equivalent changes in the 

 internal environment of the fungus. 



Drayton (1937) was able to produce the perfect stage of Botryotinia 

 convoluta by controlling light, temperature, and nutrition. The technique 

 is somewhat involved, but it should be remembered that in nature the 

 external environment varies a great deal during the course of a year. 

 Fluctuations in temperature, moisture, light, and food supply are the 

 normal result of the procession of the seasons. Drayton found autoclaved 

 W'hole wheat to be an excellent substratum for this fungus. The most 

 favorable results w^ere obtained by allowing the culture to develop at 

 14°C. in the dark for 45 days. At the end of this time the sclerotia w^ere 

 placed in moist quartz sand at 0°C. for 3 to 4 months, then stored at 

 5°C. When the apothecial fundaments were 2 to 3 mm. long, the cultures 

 were moved to a greenhouse and placed under cheesecloth and the tem- 

 perature held at 7°C. at night and below 15°C. during the day. The 

 apothecia matured within 4 wrecks. 



Yarwood (1936, 1941) observed parasitic fungi under natural condi- 

 tions and found that the production and liberation of the conidia of 

 Erysiphe polygoni and the ascospores of Taphrina deformans followed a 

 definite diurnal pattern in nature. 



The combined effects of temperature and light upon sporulation of 

 Helminthosporium gramineum are clearly shown by Houston and Oswald 

 (1946). Best sporulation was obtained under outdoor conditions, with 

 14 to 15 hr. of daylight and the average maximum and minimum tem- 

 peratures 26.8 and 8.2°C., respectively. No conidia were produced on 

 potato-glucose agar in the absence of light, either outdoors or inside. 

 Artificial light apparently was less effective than daylight. However, 

 continuous light at 13°C. allowed the formation of a few conidia. On 

 pieces of infected barley leaves, conidia were formed without exposure to 

 light, over a considerable range in temperature. As an explanation of 

 these differences, the authors believe that the mycelium in the leaf in 



