896 BIOLOGICAL EFFECTS OF RADIATION 



Gallemaerts (56), Hutchinson (81), Molz (124), Stevens and Hall (179), 

 Hall (65), Rahn (153), and Bisby (8) found that an alternation of light 

 and dark is necessary for zonation. Others, however, such as Reide- 

 meister (156) and Munk (129), found that zones are formed only in 

 continuous darkness. Hedgcock (69) and Gallemaerts (56) determined 

 the wave-lengths of light which are effective in producing zonation, but 

 their results are contradictory, even though they used the same species 

 of fungi. Light is not the only factor which may cause zonation. Bisby 

 (8), Hall (65), and Ellis (40) showed that an alternation of temperature 

 will produce zonation while Milburn (122), Hedgcock (69), Moreau (125), 

 and Ellis (40) showed that the quality of the medium may determine 

 whether or not zonation occurs. One of the most interesting discussions 

 of zonation in fungi was written by Brown (17). He noted that zonation 

 in some strains of Fusarium is dependent on light while in other strains 

 there appears to be no correlation. He gave the following conditions as 

 necessary for zonation in response to light changes : (a) the fungus should 

 be affected in its sporing capacity by light; (6) a nonstaling type of 

 mycelial growth should be maintained from day to day; and (c) the 

 medium should not be such as to permit such intense sporulation that 

 successive zones fuse. His work is valuable chiefly because of his 

 appreciation of the complex of factors involved. The influence of light 

 on zonation in fungi may differ with the species concerned, but it is 

 highly important that the influence of all factors should be evaluated 

 and that any indirect effects of light should be distinguished from direct 

 effects. 



Initiation of Fruiting and Further Development. — Fungi may be classi- 

 fied in the following distinct groups with regard to their ability to fruit 

 under different light conditions: (a) those in which fruiting is inde- 

 pendent of light; (b) those which will fruit only in the light; (c) those in 

 which light is necessary only to produce the fundaments of fruiting 

 structures; and (d) those in which light is not necessary to produce 

 fundaments but is necessary for the further development of fruiting 

 structures. A familiar example of the first group is Agaricus campestris 

 which is cultivated by mushroom growers on a large scale in caves and 

 cellars in darkness which is complete except when the cellars are visited 

 by attendants with candles or torch lamps. It is grown in this way 

 because of the better yield assured by the more uniform temperature 

 maintained in the absence of light. Other fungi belonging to this group 

 were described by Harter (66), Lendner (102), and Buller (19). Pleywdo- 

 mus and certain agarics described by Coons (25) and Lendner (102), 

 respectively, belong to group (6). Brefeld (15, 16), Holterman (cf. 

 Temetz, 187), Ternetz (187), Harter (67), and Schenck (164) cited a 

 number of different species which belong to group (c). Some of the most 

 common among these are certain Coprinus species, Tomentella, Diaporthe, 



