438 BOTANY 



been accurately investigated in relatively few forms; a number of 

 distinct types are found. 



1. In the Laboulbeniaceae (Fig. 396) the carpogonium with its 

 trichogyne, and the antheridia which produce spermatia, show a 

 striking correspondence with the structures of the same name in 

 the Red Algae. 



2. The Ascomycetes which enter into the composition of Lichens 

 (Figs. 429, 430) approach most closely the preceding group. The 

 carpogonium is here a spirally- wound filament of cells terminating in 

 a trichogyne. The spermatia are formed in special flask -shaped 

 depressions of the thallus, the spermogonia. Similar reproductive 

 organs occur in some Ascomycetes which do not form parts of 

 Lichens. 



3. Pyronema ( 69 ) (Fig. 390) and related genera, Ascodesmis 

 ( = Boudiera CLAUSSEN) ( 69 ), Mon.ascus ( C3 ), Aspergillus ( 66 ), exhibit a 

 distinct type. A multinucleate carpogonium which is provided with 

 a trichogyne is fertilised by a multinucleate antheridium, the two 

 structures being thus coenogametes (p. 429). Lachnea( Q4 ) may also be 

 placed here. 



4. In the Erysibaceae (Fig. 382) a uninucleate antheridium unites 

 directly with a uninucleate oogonium. 



Other genera exhibit transitions in the structure of the carpo- 

 gonia and antheridia from the type of the Lichen fungi to those 

 of Pyronema, and of the Erysibaceae. Thus the former may perhaps 

 be regarded as primitive Ascomycetes and the latter as reduced ( 62 ). 



In some Ascomycetes the sexual organs are present, but no fertilisa- 

 tion of the carpogonium takes place, and in others 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 the asci at 

 the ends of branches. 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 which 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). 



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 



