EFFECTS OF RADIATION ON FUNGI 895 



Morphology. — Certain morphological changes may be readily pro- 

 duced in fungi exposed to radiation. By a microscopic examination very 

 pronounced differences in the shape and appearance of fungus colonies 

 were observed by Berde (5) and Schreiber (166). Schulze (167) made 

 some very interesting microscopic observations of the mycelium of 

 Mucor stolonifer which was irradiated with sublethal doses of ultra- 



o 



violet radiation of 2900 A. About 30 min. after irradiation the hyphae 

 become densely granular, increase to almost double their usual diameter, 

 and the tips of the hyphae become bulbous or club-shaped. If not 

 irradiated too long, there appears after an interval, depending on the 

 time of irradiation and the intensity, a clear mass of protoplasm in the 

 swollen end of each hypha from which arises a new hypha. The repro- 

 ductive processes of cells are apparently hindered with much lower light 

 intensities than the growth processes. Doses which are too small to 

 prevent growth may be sufficient to stop division. This results in the 

 production of giant cells and has been observed by many workers includ- 

 ing Elfving (38), Reinhard (157), Lacassagne (96), and Holweck (76). 



FRUITING STRUCTURES 



Form. — Many of the early botanists observed that fungi which are 

 growing in dark places have quite a different shape from those in the 

 light. One of the earliest records of this change in form due to light was 

 reported by Fries (52) as early as 1821. He observed that in the dark the 

 stalks of mushrooms are longer and often branched, and unstalked 

 forms become stalked. Since observations were made in the field, it is 

 not clear to what extent other factors may have been involved. Other 

 observers including Brefeld (15), Vines (189), Holtermann (cf. Ternetz, 

 187), and Buller (19) found that a number of the Mucorales and Basidio- 

 mycetes develop elongated fruiting structures in the dark. Fries (52) 

 also observed that certain Myxomycetes, Hyphomycetes, Basidiomycetes, 

 Pyrenomycetes and truffles are not affected in their development by a 

 lack of light. These last observations have been confirmed by later 

 writers and have been found to apply rather generally to a large number of 

 families and genera. 



Zonation. — A number of investigators have studied the effects of 

 light on the arrangement of conidiophores or fruiting bodies in concentric 

 rings. The phenomenon is apparently quite complex involving the 

 interaction of a number of different environmental factors. The results 

 which have been reported are somewhat contradictory, owing probably to 

 insufficient control of environmental conditions and to the fact that 

 different species may react very differently to the same conditions. As 

 yet sufficient data from controlled experiments are not available to draw 

 definite conclusions. A number of workers including Hedgcock (69), 



