EFFECTS OF RADIATION ON FUNGI 901 



the full mercury arc was used, Hutchinson and Ashton (79) found that 

 sporulation m Colletotrichum phomoides is earlier with short exposures 

 but later with longer exposures. They observed that the time of sporula- 

 tion is an inverse expression of the growth rate only within certain limits. 

 They used a monochromator to study the effects of specific wave-lengths, 

 but since no measurements of intensity were made, the effects produced 

 by different spectral lines are not comparative. 



Abscission and Discharge. — Light produces very different effects on 

 the abscission of spores in different fungi. Coemans (cf. Elfving, 39) in 

 1859 and Brefeld (15) somewhat later were among the first to notice 

 that the discharge of spores in Pilobolus can be delayed by placing the 

 fungus in the dark. Since that time the same has been shown to apply to 

 Ascoholus, slime molds, and Coprinus by deBary (3), Hofmeister (74a), 

 and Buller (19), respectively. Buller found, however, that if the fruiting 

 bodies of Coprinus receive light daily, they do not require light on the 

 day of the expansion of the pileus and will produce spores and shed them 

 in the dark at the normal rate. Some attempts have been made to 

 determine which w^ave-lengths are important in the discharge of spores. 

 Kraus (95), Kegel (155), and Jolivette (84) have all reported that blue 

 light is the most effective but that other wave-lengths will cause spore 

 discharge to a lesser degree. 



Germination. — Qualitative studies of the effects of sunlight on the 

 germination of spores were made in 1860 by Hoffman (74) and by many 

 others since that time (3, 19, 38, 50, 90, 100, 116, 167, 182, 188, 191, 193). 

 In general, fungus spores apparently germinate just as well without light 

 and will not germinate in too strong light. Light received by spores may 

 affect the percentage germination, the time required for germination, 

 and even the ultimate growth of the culture, but it does not, in general, 

 affect the morphology of the hyphae produced. 



The inhibitory effect as measured by the percentage germination is 

 directly proportional to the intensity of radiation once a minimum 

 intensity is reached. This was emphasized by Schulze (167), Luyet (110), 

 and Rabinovitz-Sereni (151). However, as both Luyet (HI) and Smith 

 (168) have more recently pointed out, the proportionality does not hold 

 for large as well as small doses, as shown by the S-shaped survival curves 

 which they obtained. 



The data which have accumulated indicate that in general the per- 

 centage germination decreases as the wave-length decreases throughout 

 the visible and ultra-violet spectrum. Sorokin (171) and Klein (90) 

 both using liquid filters showed that blue light is the most inhibitory of 

 the visible spectrum. Laurent (100) placed spores behind screens of 

 quinine sulfate and found that ultra-violet is more inhibitory than visible 

 radiation. Bovie (13, 14) using wave-lengths ranging from the longest 

 of the ultra-violet to those of less than 1700 A concluded that destructive 

 action in the ultra-violet increases as the wave-length decreases. Certain 



