SECT. I CRYPTOGAMS 389 



of which bears, however, a multicelhilar trichogyne, may be placed 

 here. 



4. In the Erysipheae (Fig. 318) a uninucleate antheridium unites 

 directly with a uninucleate oogonium. 



It remains for future research to determine whether these types 

 are to be derived from a single one or whether they indicate a 

 polyphyletic origin for the Ascomycetes. 



In many genera the sexual oi^gans are present, but no fertilisation 

 of the carpogonium takes place, and in some groups of Ascomycetes 

 they are more or less completely reduced. 



The carpogonium does not give rise to a resting oospore, but 

 remains in connection with the parent plant ; from it ascogenous hyphae 

 or cell-filaments grow out, branch, and ultimately form at the ends 

 of branches the asci. The ascogenous hyphae and asci proceeding 

 from a carpogonium, or in some cases from a group of carpogonia, 

 form a fruit-body or fructification. In the formation of this, vegeta- 

 tive hyphae, derived from the mycelium of the parent plant, and 

 sharply distinct from the ascogenous hyphae, take part. The sterile 

 hyphae grow between and invest the ascogenous filaments. The my- 

 celium Avhich produces the sexual organs represents the sexual genera- 

 tion (gametophyte) ; the system of hyphae proceeding from the carpo- 

 gonium and ending in the asci corresponds to the asexual generation 

 (sporophyte). In this type of alternation of generations there is a 

 remarkable agreement between the Ascomycetes and the Red Algae. 



Within or on the surface of the fructifications of some groups of 

 the Ascomycetes the asci stand parallel to one another in a layer 

 called the hymenium, and between them as a rule are paraphyses 

 borne on the sterile system of hyphae of the fructification. 



In some orders of Ascomycetes the sexual organs and the 

 fructifications are completely wanting, probably owing to reduction. 

 The asci then arise directly from the mycelium. 



The ASCUS C"") originates from a single cell ; this to start with con- 

 tains two nuclei, derived from the preceding fertilisation, which fuse, and 

 the resulting nucleus by repeated division gives rise to eight nuclei. 

 By a process of free cell-formation the spores become limited by cell 

 walls in the way shown in Fig. 97 (Figs. 317, 327). In contrast 

 to the formation of spores in the sporangia of Phycomycetes the 

 cytoplasm of the ascus is not completely used up in the formation 

 of the ascospores. The spores usually form a longitudinal row, 

 embedded in the remaining epiplasm, which contains glycogen, and are 

 ultimately ejected from the ruptured apex of the ascus by the swelling 

 of this. The spores are adapted for dispersion in the air. 



The behaviour of tlie sexual nuclei in and after fertilisation of the carpogonium 

 is only accurately known in a fe;v cases. For some Ascomycetes {Pijronema and 

 Monascus) it has recently been shown tliat the sexual nuclei do not fuse in the 

 carpogonium, but lay themselves side by side. In tlie ascogenous hyphae the 



