28 SEXUAL REPRODUCTION IN CERTAIN MILDEWS. 



apogamous fructification of Dipodascus, it is interesting to note that 

 Juel insists that the spore-sac of Dipodascus corresponds to the entire 

 cell complex which arises from a fertilized carpogonium. The nuclear 

 fusion in Dipodascus corresponds to the sexual fusions in the carpogo- 

 nium and not to those in the asci. This is the view adopted by Wager 

 (97), and in his more recent discussions Dangeard (21) has given up 

 his earlier position, since plainly the individual asci in his fig. 5, p. 55, 

 do not correspond to the fructifications shown in fig. 4, p. 154. With 

 this the contention that the ascus is an egg becomes still more incon- 

 sistent. In adopting this latest conception that the ascogonium and 

 ascogenous hyphse constitute a gametophore derived by growth and 

 branching from a gametangium which has ceased to produce motile 

 gametes in adaptation to a terrestrial habit, Dangeard admits De Bary's 

 contention that the ascocarp is a unit morphologically comparable in its 

 initial stages to one or more pairs of oogonia and antheridia. He thus, 

 in reality, rejects his earlier conception that each ascus is an egg and 

 morphologically the equivalent of a hypothetical parthenogenetic fruit- 

 body of the lower fungi or algae. Dangeard now inclines to the view 

 that the ancestry of the Ascomycetes is to be sought in the Oomycetes ; 

 and the real conclusion from his argument, admitting his premises, is 

 that the ascogonium and ascogenous hyphae are vegetative outgrowths 

 from a parthenogenetic egg and that the ascus is a new structure in 

 which this vegetative development ends. 



Dangeard (21) maintains that he can not find the stage when fusion 

 takes place in Pyronema, but negative evidence on a point of this kind, 

 when unaccompanied by positive results as to further details of cell and 

 nuclear structure and behavior, are of little value. Meanwhile, we may 

 be sure that morphologically, in* its relation to the fruiting bodies in 

 other groups of fungi or algse, the ascocarp is to be interpreted as origi- 

 nating from a sexual apparatus. This fact will not be altered by the 

 discovery of forms in which, by apogamy or parthenogenesis, the sexual 

 cells have either been modified in form or become functionless. 



I am unable to find anything in the discussions of Dangeard to 

 invalidate the conclusions which I reached in a former paper (40) as 

 to the morphology of the ascocarp. Further, the positive results briefly 

 summarized above — obtained, as they are, by different workers and on 

 widely separated forms — certainly favor the conclusion that the sexual 

 organs of the Ascomycetes are regularly functional ; and when we con- 

 sider the difficulties involved in actually working out every stage in the 

 development of an ascocarp from its earliest inception, it is not sur- 

 prising that our knowledge has not advanced more rapidly. 



