GROUP I. THALLOPHYTA : FUNGI. 295 



ROMYCETES, or Yeast-Fungi, which is familiar on account of the alcoholic 

 fermentation of saccharine solutions which some of its members excite (e.g. 

 Saccharomyces Cerevisice used in brewing, and S. eHipsoideun which causes 

 the fermentation of the grape-juice in the manufacture of wine: see p. 198). 

 The plant is usually a single small spherical or oval nucleate cell, and 

 multiplies rapidly by gemmation (Fig. 174: see p. 149). When budding is 

 proceeding very rapidly, the successive cells may remain coherent for a 

 time; but a true mycelium is only rarely found, as in S. Mycoderma, 

 which forms a scum on decomposing wine and beer. 



Under certain conditions, particularly the absence of a sufficient supply 

 of food, the plant forms spores. Usually four spores are formed in a cell, 

 by free cell-formation, from a portion of the protoplasm, the rest remain- 

 ing as a parietal layer of epiplasm. The spores surround themselves with 

 a membrane, and are set free by the disorganisation of the wall of the 

 cell. The spores retain their vitality under conditions, such as desicca- 

 tion, absence of food, extremes of temperature, etc., which would prove 

 fatal to the Yeast-plants. The spores germinate, on attaining appropriate 

 conditions of moisture and temperature, and give rise to Yeast-cells by 

 budding. 



Inasmuch as the formation of the spores in a Yeast-cell takes place in 

 the same manner as the formation of spores in 

 an ascus, the Yeast-cell may be regarded as an 

 ascus. It is on this account that the Saccharo- 

 mycetes are included in the Ascomycetes, and in 

 the Gymnoascese on account of their naked asci. 

 They are, however, reduced and sexually de- 

 generate forms. 



It must be borne in mind that cells very Fio. 174,-BuddinR cells 



similar to those of the true Saccharomycetes, of Yea8t J*^***"**" 



..-.., if Cerevisue) ; the clear spaces 



multiplying in the same manner, and often in thfl ce]lg are vacuo ] es> 



capable of exciting the alcoholic fermentation (x300.) 

 of sugar, may be formed by gemmation from 



the conidia of various kinds of higher Fungi (e.g. Mucor racemosus, Peni- 

 cillium glaucum, some Ustilaginese and Basidiomycetes) under special 

 conditions. These Yeast-like cells, however, grow into mycelia -under 

 appropriate treatment. However, it is still a question whether all the 

 forms of Saccharomycetes may not be merely secondary cpnidial forms of 

 gernmse of mycelial Fungi. 



Order II. Pyrenomycetes : asci forming a hymenial layer, with an 

 investment; the ascocarp is either a cleistothecium or a perithecium; a 

 stroma is present in some families. 



The ascocarp is a cleistothecium in the sub-order Perisporiacese, includ- 

 ing the families Erysipheae (the Mildews) and Perisporieae (e.g. Eurotium 

 and Penicillium) ; in these families there is no stroma. 



Eurotium Aspergilhis is the greenish Mould which so often attacks jam. 

 It can be well cultivated for study on stewed prunes, by sowing conidia 

 obtained from infected jam. The prunes soon become covered with a 

 white, dowjiy substance, which is the vegetative mycelium ; this grad- 



