70 PAKASITES BELONGING TO THE GENUS GLOMERELLA. 



factor either determines trie production of perithecia, though a fruit- 

 ing strain will fruit more abundantly and freely on some substrata 

 than on others. 



It has also been suggested that the nearness or remoteness of origin 

 from ascospores of conidia used in any particular series of cultures 

 might be a factor of importance in determining the course of develop- 

 ment of such cultures. The data bearing upon this question which 

 we have obtained from our pedigreed pure-line cultures carried 

 through several generations do not appear to support this theory, 

 though perhaps the available data are not sufficiently numerous to 

 justify definite conclusions. 



Of a similar nature is the idea that the production of ascogenous 

 forms occurs only at intervals after the virility or vitality of the coni- 

 dial or pycnidial form has been greatly reduced by continuous asexual 

 reproduction. There is no known evidence to support this view. 

 Whether there is an actual or potential sexual stimulus or union of 

 nuclei involved in the production of perithecia in Glomerella is not 

 known. No work has been done on the cytological features of the 

 development of the perithecia. As perfect fertile perithecia are pro- 

 duced in abundance in pure cultures from single spores, either conidia 

 or ascospores, it seems certain that no fertilization or union of nuclei 

 between different individuals is necessary. Whatever nuclear unions 

 take place must be between nuclei of the same individual, as is known 

 to be the case in some other ascomycetes. 



The most general supposition has perhaps been that which predi- 

 cated the production of perithecia as dependent upon certain condi- 

 tions of nutriment or other environment of the organism. This has 

 led to the trial, by most investigators, of various culture media of 

 different constituents in different proportions and also the submission 

 of cultures to various conditions of temperature, air, light, and 

 moisture. Very little success with pyrenomycetous fungi has ever 

 been attained in this direction. In no case have the writers been 

 able to cause perithecia to appear in cultures which did not produce 

 them when grown on com-meal agar under ordinary laboratory con- 

 ditions. So far as we have been able to determine, no cases have 

 been reported in which the evidence was sufficiently conclusive to 

 prove that perithecia were produced in artificial cultures as the 

 direct result of modifications of the culture media. Smith (83) 

 reports that the formation of perithecia in a fertile race of Neocos- 

 mospora was prevented by the use of strongly alkaline media, but no 

 nonperithecia-forming strains were made to produce perithecia by 

 change of medium. 



Appel and Wollenweber (1), in discussing this problem as it relates 

 to Fusarium, Nectria, Neoeosmospora, etc., have made some very 

 ingenious suggestions in attempting to account for the production or 



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