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MONOGRAPH OF THE LABOULBENIACE^E. 



in any attempt to trace the homologies of the ascus or the derivation of the group of 

 Ascomycetes in general. 



It is not my intention in this connection to enter into any detailed discussion of 

 the several theories which have been advanced in regard to these matters ; yet they 

 cannot be allowed to pass unnoticed. In brief, it may be said that, as regards the 

 primary origin of the Ascomycetes, authorities seem generally agreed in deriving 

 them, in an ascending series, from the Phycomycetes ; but in the discussion of the 

 homologies of the reproductive organs in either case, the agreement has not been 

 so striking. De Bary, as is well known, relying in a great measure on his observations 

 in regard to the development of Sphaerotheca, as well as on the account given by 

 Eidam of his genus Eremascus, finds little difficulty in homologizing (with his usual 

 judicious cautiousness of statement) the asci of these genera with the oogonia of 

 the Phycomycetes ; while their sexual derivation was further substantiated through 

 the studies of Janczewski and others on Ascobolus, by those of Kihlman and others on 

 Pyronema, by those of Stahl on the Collemaceoe, as well as by further observations 

 which need not be here enumerated. In later years there has been a reaction from 

 this view, for the most part due to the very important, yet unconvincing, researches 

 of Brefeld. This writer, by the accumulation of a large amount of wholly negative 

 evidence, having discarded as without significance the positive evidence just referred 

 to, presents an argument from which he concludes that although the Ascomycetes 

 have originated from the Phycomycetes, they have lost all traces of sexual organs. 

 According to this view, the ascus is assumed to be merely a modified non-sexual spo- 

 rangium, homologous with the non-sexual sporangia of the Phycomycetes ; and an 

 attempt is made to substantiate this assumption by the citation of a series of 

 examples which, in his opinion, illustrate the actual process of evolution by which 

 this transformation has been brought about. 



In still more recent years, observations made by Dangeard on the phenomena of 

 nuclear fusion in the Ascomycetes and elsewhere, prior to spore formation, have led 

 this writer to believe that oosporic sexuality, thus expressed, is general among the 

 higher fungi, including the group in question ; a view which, for reasons that need not 

 here be considered, does not seem to call for serious consideration. 



It is thus apparent that the question under discussion has resolved itself into the 

 phyllogeny, not of the Ascomycetes, but of the ascus ; one " school " asserting its non- 

 sexual character, the other the reverse. Supporters of the former contention, like 

 Van Tieghem, for example, seeing in the trichogyne of Stahl a remarkably developed 

 "ventilating apparatus," or in the " carpogonium " of Ascobolus or Pyronema, a 



