746 



FUNGI 



either at the same time or in irregular succession from the 

 same mycelium. A very large and heterogeneous collection of 

 fungi, classified in systematic works as ' Fungi imperfectly appear 

 to be conidial forms of imperfectly known Ascomycetes, the 

 ascospores of which are either absent altogether or which have 

 not yet been recognised. 



2. The True Yeasts are by several authorities included in 

 the Ascomycetes and united into an order or family, the 

 Saccharomycetacece. The commonest and best known species 

 is Beer-yeast {Saccharomyces cerevisia Meyen). No true hyphae 

 or mycelium is produced, the plants in a vegetative state con- 

 sisting of single oval cells, which, under some conditions of 

 nutrition may become considerably elongated and partially 

 resemble a hyphal filament. 



Each oval yeast-cell has a distinct cell-wall, and is filled 



with granular proto- 

 plasm in which are 

 visible larger or 

 smaller vacuoles (Fig. 

 253). Multiplication 

 takes place by the 

 process of budding or 



Fig. 253.— I. Cells of common \itxc-yeas.1(Saccharomyces Sprouting (sCC p. 680), 

 «rOT«!« Meyen) ; 2, 3, and 4, successive stages of ' bud- , .,,.,. 



dmg' process of multiplication i 5, cells containing endo- ^°Q especially IS thlS 



spores (all enlarged about 750 diameters). .1 , , 



the case when the 

 cells are well nourished in solutions of saccharine substances, such 

 as malt-extract. When the cells are poorly nourished and grown 

 at a temperature of about 30° C. on moistened slabs of plaster of 

 paris, the protoplasm within each of them divides and forms 

 from two to four endospores : the whole cell thus becomes 

 transformed into a sporangium, which is considered a simple 

 form of ascus (5, Fig. 253). 



Many conidia of fungi are capable of ' budding ' in a manner 

 similar to the true yeast-fungi and may greatly resemble the 



