320 PART IV. — VEGETABLE TAXONOMY. 



considerable size is formed ; on the upper surface is developed 

 a hymenial layer of closely compacted erect hyphal branches ; 

 the whole sporocarp gradually assumes the form of a cup, and 

 many of the hyphal branches in the hymenium develop into 

 eight-spored- asci. Fig. 521 is a diagram of one of the sporo- 

 carps, and Fig. 522 illustrates some of the asci in various stages 

 of development. 



The Saccharomycetes, as has already been stated, are now 

 classed among the Ascomycetes and are regarded as degenerate 

 members of the group. They include most of the forms which 

 are capable of exciting the alcoholic fermentation in saccharine 

 liquids. They are minute plants of very simple structure, con- 

 sisting of rounded or ellipsoidal a 

 cells, which either occur singly or 

 loosely united into short chains. 

 The cells are non-nucleated, or, at 

 any rate, no nucleus has yet been °\jt 

 observed in them ; they contain a 

 vacuole, and, when growing in a 

 suitable medium, they increase rap- 

 idly by budding or sprouting. This 

 is their principal and, under ordi- 

 nary circumstances, their only mode FlG 523 _ Yea st cells, a, cells 

 of increase, but when deprived of ^g^X^^t^'oiT, 

 sufficient nourishment, as for exam- %^?£^ S i^S$S* 

 pie when wine-ferment is cultivated about 700 diameters. 

 for several days on a porous tile kept moist under a bell-jar, 

 the cells cease sprouting and the contents break up into asco- 

 spores, from two to four of these being produced in each 

 cell. 



When growing in saccharine solutions they decompose the 

 sugar mainly into alcohol, which remains in solution, and carbon 

 dioxide, which escapes as gas. They have the peculiarity of 

 being able to do without free oxygen, providing sugar is present 

 in solution. 



The best known members of the group are Saccharomyces 

 Cerevisiae, or brewer's yeast; S. ellipsoideus, or wine-ferment; 

 S. albicans, the ferment which produces thrush, but which, 

 under certain conditions, is also capable of exciting the alco- 



