INTRODUCTION 211 



the trichogyne fuse with it, the sperm nucleus entering and passing from 

 cell to cell until it enters the oogone. In other cases the trichogyne fuses 

 with an antherid without the formation of separate sperm cells and the 

 nucleus or nuclei from the antherid enters the trichogyne and eventually 

 reaches the oogone. All degrees of reduction may be found from a multi- 

 cellular ascogonium with a long trichogyne to a one-celled oogone and 

 one-celled trichogyne as it occurs in Pyronema. In many cases the tricho- 

 gyne is lacking, so that the antherid comes into direct connection with 

 the oogone. Sometimes no antherid at all is formed. In such a case pairing 

 of the nuclei often does not occur in the oogone but the female nucleus 

 divides and the nuclei pass out in pairs into the ascogenous hyphae. In 

 Asco'phanus granulatus (Bull.) Speg. {Humaria granulata Quel.), which 

 does not possess an antherid, Gwynne-Vaughan and Williamson (1930) 

 report that the oogone nuclei unite by pairs and the resultant zygote 

 nuclei enter the ascogenous hyphae. Apparently a cell of the series of 

 ascogonial cells may in some cases be substituted in function for an 

 antherid, its nucleus taking the place of the antherid nucleus. Sometimes 

 no recognizable oogone or ascogonial cells can be found. Some of the 

 vegetative hyphae of the spore fruit become converted in a manner not 

 known into ascogenous hyphae with dicaryon cells. In many families of 

 the Ascomyceteae the terminal cell or cells of the ascogenous hypha 

 become asci without the formation of a hook as described above in Pyro- 

 nema. The two nuclei of the cell fuse and the cell enlarges terminally or 

 laterally, with successive nuclear divisions and ascospore development. In 

 the sexual species of the order Saccharomycetales two cells fuse to form 

 a single ascus and no ascogenous hyphae are produced. Kharbush (1927) 

 reports^ a similar origin of the asci in the highly developed apothecium 

 of Botryotinia fuckeliana (de Bary) Whetzel. In this apothecium, according 

 to him, there are no distinguishable ascogenous hyphae. At the base of the 

 hymenium the apices of adjacent hyphae unite and the nuclei fuse, thus 

 giving rise to the young asci, one fusion of paired hyphae for each ascus. 

 Greis (1940) has found a quite similar origin of asci in two species of 

 Morchella studied by him. In the subhymenial layer, or shortly below it, 

 terminal multinucleate cells of adjacent vegetative hyphae unite and 

 grow out to form a stouter binucleate cell, with one nucleus contributed 

 by each hypha. This cell may enlarge and become the ascus or the nuclei 

 ma> divide conjugately with the production of a short ascogenous hypha, 

 whose terminal cell becomes the ascus, without the formation of the 

 usual hook. The opposite extreme is found in some species of Taphriiia 

 {Exoascus) in which Miss Wieben (1927) has shown that the ascospores 



2 In view of the entirely different mode of sexual reproduction reported by Drayton 

 (1934) for Stromatinia gladioli (Drayton) Whetzel it is evident that the process in 

 Botryotinia fuckeliana needs re-examination. 



