104 MORPHOLOGY AND LIFE-HISTORY OF YEASTS. 



This family comprises three genera : Monospora, SarrJiaru- 

 myces and Schizo-Saccharomyces. As the name implies, the 

 first genus is characterised by the fact that each ascus contains 

 only a single spore. Up to the present only one species of this 

 genus is known, namely Mono^pom cui^pidafa (discoA'ered by 

 Metschnikoff), which is parasitic on and fatal to Daphnidfe ; it 

 is, however, beyond our province. Henceforward we have 

 merely to deal with the other two genera, Sarcharomyres and 

 S('lii':o-Sac('liaromyces. Of the latter, only a few species are as 

 yet known. Some of these are, nevertheless, worthy of attention, 

 either from their technical importance, or from a physiological 

 standpoint, and will therefore be dealt with in a separate 

 chapter as soon as our main task is accomplished, namely the 

 study of the most important of the numerous species belonging 

 to the genus Saccharomyces. In these latter the reproduction of 

 the cells is effected by vegetative means ; and under normal 

 conditions almost exclusively by the process of budding described 

 in § 219. An example is shown in Fig. 124. In the Schizo- 

 Saccharomyces on the other hand — as will be more fully 

 elucidated later on — this process retires into the background 

 and gives place to another, which closely resembles the repro- 

 duction of bacteria by fission, as was described in § 42. In this 

 case, instead of putting forth, like Saccharomyces, a bud which 

 grows to the same shape and size as the mother-cell from which 

 it sooner or later becomes detached, the cell develops a trans- 

 verse partition wall, which then divides into two layers ; and as 

 soon as this is effected there is nothing to hinder the separation 

 of the resulting daughter-cells (see Fig. 125). It is owing to 

 this behaviour that the genus received the name Schizo-Saccharo- 

 myces. 



The substance of the foregoing remarks can be employed 

 for drawing up a scheme for subdividing the Saccharomycetes 

 family : — 



Saccharo- 

 mycetes 

 (Ascomy- 

 cetes with 

 naked asci, " 

 the myce- 

 lium itself 

 acting as 

 an ascus) 



The ascus develops only a single spore . 

 f{a) Vegetative re- 

 production by 

 budding. 



(/3) Vegetative re- 

 production by 

 fission . . . 



[b) Ascus Polysporous \ 



Genus. 

 Monospora. 



2. Saccharo- 

 myces. 



Schizosacch- 

 aromyces. 



Before entering upon the morphology and progress of de- 

 velopment of the genus Saccharomyces, we will first occupy 

 ourselves, in the following paragraphs, with the question of the 

 alleged descent of the Saccharomycetes from other fungi ; at 



