242 THALLUi'HyTE!^. 



differentiated into an outer firm layer and an inner one capable of swelling in water. 

 The wall is generally of a dark colour, but seldom or perhaps never actually lignified ; 

 it is usually tough, rarely hard and britde. An important part is also played in 

 Fungi by the formation of mucilage through the softening and swelling of the outer 

 layers of the walls of the hyphae. This occurs either in all the hyphae of a Fungus, 

 by which it acquires a gelatinous appearance, as among the Tremellini, or separate 

 portions or layers of a larger mass of hyphae are subsequently converted into muci- 

 age, the inner structure of many Gasteromycetes, as has already been mentioned, 

 iepending on this change. This formation of mucilage takes place even on the 

 jpores, so that their mode of dissemination takes the form of a trickling mucilage 

 n which they are enveloped (as in Sphacelia and Phallus). But most commonly 

 he spores fall off dry, or are expelled singly or in masses, or are thrown out with 

 /iolence {e,g. Pilobolus, Ascobolus, Sphaerobolus). 



Since the labours of Tulasne, De Bary_, Woronin, and others, the Systematic Grouping 

 of Fungi, as that of Algae, has been completely remodelled. Whole sections of genera 

 of the earlier systems are now recognised as simple forms of development in the alterna- 

 tion of generations of other forms, and the same fate is still threatened to many apparent 

 species and genera. At present the classification proposed by De Bary, which corresponds 

 to the present state of science, must be retained. The class of Fungi is thus divided into 

 the following groups: — 



I. Phycomycetes. 



Saprolegnieae. 



Peronosporeae, 



MucorinL 



II. Hypoderraiae. 

 Uredineae. 

 Ustilagineae. 



III. Basidiomycetes. 



Tremellini. 



Hymenomycetes. 



Gasteromycetes. 



IV. Ascomycetes. 



Protomyces. (?) 



Tuberaceae. 



Onygeneae. 



Pyrenomycetes- 



Discomycetes. 



The characters of each more important division will be Illustrated in the following 

 pages by ofte or two examples. 



I. Phycomycetes. In its morphological phenomena this order resembles Vau- 

 cheria. The Saprolegnieae and Peronosporeae form spherical oogonia at the ends of 

 the mycelial branches, in each of which one or more oospores result from fertilisation. 

 In (i) the Saprolegnieas^ which mostly grow on the bodies of insects putrefying in 

 water, an alternation of generations takes place between the asexual individuals — which 

 are the first formed and recur many times forming swarm-spores — and the sexual 



^ Pringsheim in Jahrb. fur wissen, Bot. vol, I. p. 289, and vol. II. p. 205. — Hildebrand, ditto, 

 vol. VI. p. 249. — Walz, Bot. Zeitg. p. 537, 1870. — Leitgeb, Jahrb. fiir wisseri. Bot. vol. VII. p. 357. — 

 Reinke in Schultze's Archiv fiir mikrosk. Anat. vol. V. p. 183. 



