94 MANUAL OF BOTANY 



The Phycomycetes form the lowest group and include all 

 the forms which as well as asexual show sexual reproduction 

 by fusion of differentiated gametes. They thus include the 

 Mucorini, the Peronosporeae, and the Saprolegniaceae. 



The Mesomycetes comprise the intermediate forms between 

 the Phycomycetes and the Ascomycetes and the Basidiomycetes 

 respectively. They approach the latter in their vegetative organs, 

 especially their incompletely septate mycelium. They differ from 

 them in not possessing definite asci or basidia. They have no 

 sexual organs, differing thus from the Phycomycetes. 



The Hemiasci are a small and comparatively unimportant 

 group ; the Hemibasidii include the Ustilagineae, or smuts. 



Through the Mesomycetes the line of descent passes to the 

 Ascomycetes on the one side and the Basidiomycetes on the 

 other, which together form the group of the Mycomycetes. 

 These have septate hyphae, and produce their spores at some 

 time or other in asci or on basidia. Sexual reproduction is un- 

 known. 



The Ascomycetes embrace, generally speaking, the forms 

 included under the same name in the older classification, except 

 that the Saccharomycetes are excluded. The Ascolichenes are 

 held to belong to this group and are not put into a separate 

 class. The Ascomycetes are divided into two series, the 

 Exoasci, where the asci are simple and free, and the Carpoasci, 

 where they are gathered into the various forms of fructification 

 already described. 



The Basidiomj'cetes are a larger group than in the old 

 system, as the ^cidiomycetes are included in it. The latter 

 are referred to the series Protobasidiomycetes on account of the 

 mode of germination of the teleutospore, which gives rise to 

 what was formerly called a promycelium on which were borne 

 sporidia. This promycelium is held to be a 2^^'otohasidium, 

 from each cell of which a basidiosporeis segmented. The Auto- 

 basidiomycetes comprise what under the older system were 

 called Basidiomycetes, except the Auriculariaceae and the Tre- 

 mellacese, which form with the Uredineae the first series. 



The Basidiolichenes are held to be members of this group, 

 though not referable to either of the two series. 



Finally, the Saccharom^^cetes are separated from the rest on 

 the ground that their life history is very imperfectly known, 

 and that they probably are only stages in the life cycle of some 

 polymorphic form of the higher Fmigi. They are classified as 

 an additional group under the name Fungi imperfecti. 



