GROUP I. THALLOPHYTA : FUNGI. 279 



nation of generations can generally be traced ; thus, in the Phy- 

 comycetes, the plant is the gametophyte, and the sporophyte is 

 either merely the oospore or zygospore, or it is the comparatively 

 small mycelium (promycelium) developed on germination from the 

 sexually-produced spore ; similarly, assuming the sexuality of the 

 group, in the simpler forms of the Ascomycetes, the plant is the 

 gametophyte, and the ascocarp the sporophyte. In these simpler 

 cases the only complication introduced into the life-history is that 

 due to the fact that, as in many of the Algae, the gametophyte 

 reproduces itself by means of asexually-produced gonidia, and 

 may not produce sexual organs ; so that there may be a succession 

 of potential gametophytes before the actual gametophyte presents 

 itself. 



In the life-history of some of the forms which have become 

 asexual through sexual degeneration (e.g. many Ascomycetes, 

 JEcidiomycetes, Saprolegniaceae), it is still possible to recognise the 

 gametophyte. It is that form which gives rise to the structure 

 which is identical or homologous with the product of fertilisation 

 in the allied sexually complete forms. For instance, in the Sapro- 

 legniacese, that form which bears the organs in which the partheno- 

 genetic oospores are formed, is the gametophyte ; similarly, in 

 the sexually degenerate Ascomycetes, the form which bears the 

 ascocarp is the gametophyte ; and again, in the JEcidiomycetes, 

 the form which produces the ascidium is the gametophyte. 



In some Ascomycetes (e.g. Claviceps), and most ^Ecidiomycetes 

 the life-history is further complicated by the polymorphism of 

 the gametophyte. Here the life-history of the gametophyte pre- 

 sents one and sometimes two (most ^Ecidiomycetes) entirely 

 asexual gonidia-bearing forms. 



In the life-history of the Basidiomycetes there is no form homo- 

 logous with the sporophyte of any of the other groups of Fungi ; 

 the sporophyte is entirely unrepresented. The plant is therefore 

 a gametophyte, and it is in some cases polymorphic. As it is 

 altogether asexual, it corresponds to the asexual forms of the 

 gametophyte in the life-history of those Ascomycetes and -5Ccid- 

 iomycetes in which the gametophyte is polymorphic. 



The foregoing account of the life-history of the higher Fungi is based upon 

 the assumption that, in the Ascomycetes, the ascocarp is the product of a 

 sexual process, or is the homologue of such a product. If, however, the view 

 be taken that the Ascomycetes are altogether asexual, then the ascocarp may 

 be regarded, not as the sporophyte, but as simply a special form of gonidiophore 



