252 THE AMERICAN NATURALIST. [Vol. XXXIX. 



first account of this phenomenon describing it for several forms. 

 The mother cell of an ascus sometimes terminates a hypha but 

 more commonly is situated a little back from the end at a point 

 where the hypha bends abruptly like a knee. The mother cell 

 contains two nuclei, closely related to each other, that unite, 

 after which the fusion nucleus divides to form the ascospores. 

 Dangeard considered this fusion to be a sexual act and the 

 product an oospore which germinates immediately to form the 

 ascus. He regards the ascus as a sporangium, and equivalent 

 to the promycelium which he calls a conidiophore. Dangeard 

 is not willing to accept any of the evidence that the ascocarp 

 ever results from a sexual act or that sexual organs either func- 

 tional or abortive are present at any stage in the life history of 

 Ascomycetes. Sexuality, according to him, is reduced to the 

 fusion within the ascus alone. He (Dangeard, 'gd-'g/a, b ; 

 : 00) discredits the work of Harper on Sphaerotheca, Erysiphe, 

 and Pyronema and the older accounts of De Bary and his pupils 

 on sexual organs of the Ascomycetes. A series of short papers 

 in Le Botaniste (: 03, Fas. i) presents Dangeard's last attack on 

 the work of Harper and a reaffirmation of his peculiar views. 



Harper's description of sexual processes in Sphaerotheca ('95 ; 

 '96) Erysiphe ('96), and Pyronema (: 00b) are so convincing 

 that, together with our knowledge of sexual organs in the 

 lichens, Laboulbeniales, and Gymnoascales, we must accept the 

 old view of De Bary that the ascocarp represents a development 

 (probably sporophytic) from a sexual phase even though it may 

 be established that there is much apogamy in the Ascomycetes. 

 Harper gives the clearest account of the nuclear fusion in the 

 ascus of any author without, however, committing himself to 

 speculations on its significance. The subject is well sum- 

 marized in his paper on Pyronema •(: 00b, pp. 363, 394). He 

 finds in Erysiphe, Pyronema, and some other forms that the 

 ascus is always developed from a penultimate cell of a hypha 

 which bends sharply so that this cell appears to lie at the tip. 

 There are two nuclei at the end of the ascogenous hypha and 

 these divide simultaneously in a very characteristic manner so 

 that the young ascus receives two of the resultant four nuclei, 

 but each is derived from a different one of the original pair and 



