THE FUNGI WHICH CAUSE PLANT DISEASE 



241 



white center of the spot. In five hours more they are so numerous 

 as to give a blackish appearance. 



In New York, Reddick found that the asci begin to ripen in May 

 and continue to mature throughout the summer being still abundant 

 in October. The asci swell in water often to twice the length 

 given above; spores are forcibly ejected from the 

 asci at maturity, being thrown to a height of 

 2 to 4 cm. There is at one end of the asco- 

 spore a hyaline vesicle which probably aids in 

 fixing it to the host.^^^ They germinate but 

 slowly, requiring from thirty-six to forty-eight 

 hours to show germ tubes. Reddick deter- 

 mined the incubation period on fruit as from 

 eight to twenty-one days and found that only 

 tender leaves still growing are susceptible. 

 The berry is susceptible even after the calyx 

 has fallen. The pycnidial spores are said by 

 some to show a hyaline appendage ^®^ though 

 others by careful study fail to find it.''" 

 These spores often live over winter.*^ The Fiq. 176.— g. bid- 



. ,. 1.11 1 • • T • .1 wellii; 26, nearly ma- 



microcomdia which develop m pycnidia similar ture ascus with 

 to those of the macroconidia do not occur so IgcoIpOTfa'i' 2«!^g"r- 

 abundantly early in the season as they do minating ascospores, 

 later and seem to be mainly limited to the pressoria. After 

 fruits. Sporeless pycnidia, pycnosclerotia, also 

 occur and may eventually develop into perithecia. Conidia on 

 hyphse of questionable relationship to the fungus are sometimes 

 seen. 



Reddick ^^° secured pure cultures in the following ways. 



1. In poured plate dilution of asci; some twenty days were 

 required. 



2. By inverting a plate of sterile agar over a bunch of mature 

 mummies floating on water. The ejected ascospores thus clung 

 to the agar and gave pure cultures in ten days. 



3. By aseptic transfer of the mycelium. 



4. By aseptic transfer of pycnospores. 



Artificial infections have been reported in Europe from both 

 conidia and ascospores: Reddick, who made many thousand in- 



