INDUCTION OF SALTATIONS 145 



same medium but were always sparse. Stevens (1931) induced 

 Colletotrichum lagenarium to form the perithecial stage in cul- 

 ture, whereas this stage had never been observed previously under 

 any conditions. Although he did not regard temperature as a 

 significant factor, he noted that the presence in the medium of 

 such sugars as favor growth also favors increased spore produc- 

 tion after irradiation. 



There is evidence that ultraviolet radiation may hasten sporula- 

 tion [Hutchinson and Ashton (1930)]. Short exposures induced 

 Colletotrichum phomoides to sporulate earlier, and long exposures 

 delayed sporulation. Hutchinson and Ashton concluded that 

 within certain limits the time of sporulation is an inverse expres- 

 sion of the rate of growth. 



EFFECT OF X-RAYS 



Both ultraviolet and X-rays have been used as therapeutic 

 agents, especially in dermatomycosis and actinomycosis. The 

 medical aspects of their use appear to be better known than their 

 general effects on fungi. The evidence concerning X-rays indi- 

 cates that fungi are rather insensitive to their action but that large 

 dosages are lethal. Haskins and Moore (1934) found that soft 

 X-rays were 2.1 times as potent in killing conidia of Penicillium 

 as were hard X-rays. The soft X-rays used by them had a wave- 

 length of 1.3 to 1.5 A; the hard ones, from 0.18 to 0.21 A. Lethal 

 action of X-rays against plant pathogens was earlier reported by 

 Pichler and Wober (1922), who successfully freed wheat seed 

 from Ustilago tritici, barley seed from U. mida, and potato 

 tubers from Synchytrhnn (Chrysophlyctis) endobioticam. 



Nadson and Philippov (1925) suppressed the formation of 

 zygotes in Mucor genevensis and Zygorhyn chits moelleri by 

 exposure of cultures to X-rays. Marked changes in protoplasmic 

 structure resulted in Sac char omyces cerevisiae and Nadsonia ful- 

 vescens after exposure to X-rays [Nadson (1937)]. 



INDUCTION OF SALTATIONS 



None of the effects of radiation which have thus far been 

 given consideration in the present account can be regarded as 

 mutations, for evidence is lacking that they are heritable. Radia- 



