EFFECTS OF RADIATION ON FUNGI 897 



Ascophenes, and Bolhitius. Pilobolus microsporus as described by 

 Brefeld (15, 16) belongs to group (d). 



The wave-lengths which are most effective in causing fruiting in those 

 species for which light is essential were studied by Brefeld (16), Klein 

 (90), Elfving (39), Lendner (102), and Luyet (111). These experiments 

 vary widely in accuracy and there are no general conclusions which can be 

 drawn. Kegel (155), Brefeld (16), and Lakon (98), however, all found 

 that the blue region of the spectrum is most effective for the development 

 of fundaments of fruiting structures. They used liquid filters and Lakon 

 also used glass filters. Kegel studied Pilobolus, Lakon Coprinus, and 

 Brefeld observed both forms. 



The exposures necessary to induce the formation of fruiting bodies 

 (in fungi from group c) are apparently very short according to Brefeld 

 (15), Lehman (101), and Schenck (164). Kobinson (159) and Schenck 

 (164) have both studied in some detail the effects of light intensity on 

 the production of fruiting bodies. They found that the duration as well 

 as the mtensity is important. Kobinson reported that within the 

 limits employed the time necessary for the production of oogonia and 

 antheridia in Pyronema confluens is proportional to the intensity. He 

 also noted that light energy can be utilized in the production of repro- 

 ductive structures only if a check to vegetative growth has previously 

 occurred. This check leads to the initiation of potentially reproductive 

 branch systems. If light falls on the culture shortly before the actual 

 check, it appears to be available for subsequent utilization, whereas if it 

 is received later than the growth check, more energy appears to be 

 necessary to produce the same results. 



In certain cases cultures may react differently to light depending 

 on the medium x)n which they are growing. As an example of this 

 Lendner (102) cited Mucor flavidus which forms sporangia in the dark 

 only if it is growing on a solid medium. 



Growth Rates. — Light may determine not only whether fruiting bodies 

 are formed but also the rate at which they develop. The sporangiophores 

 of Phycomyces nitens are exceedingly sensitive to changes in light inten- 

 sity. Bullot (cf . Klebs, 88) showed that the sporangiophores grow faster 

 in continuous light than in the dark. Later Blaauw (9) studied the 

 effects of varying light intensities. He observed that the sporangiophores 

 respond to an increase in intensity by a temporary increase in the growth 

 rate. This is followed by a decrease and brief fluctuations until the 

 original rate is regained. With one-sided illumination Oehlkers (138) 

 reported that only the first maximum appears. In either case to produce 

 a new stimulation of growth it was found that the intensity must be 

 again increased by a definite amount. Blaauw (9) found that the 

 sporangiophores become increasingly sensitive to stimulation by light 

 the longer they are kept in the dark. ToUenaar and Blaauw^ (cf. Castle, 



