THE FUNGI 



165 



SUBCLASS II. ETJASCE^: 

 Order I. Protoascineae 



The lowest of the Euasceae, the Protoascineae, comprise two fami- 

 lies, the Saccharomycetacese and the Endomycetaceae. The former 

 include the Yeast-fungi, whose relation to the Ascornycetes is some- 

 what doubtful ; the second 

 family includes a small 

 number of very simple but 

 unmistakable Sac-fungi. 



D 



n 



Yeast-fungi. The Saccha- 

 romycetacese or Yeast-fungi, 

 unlike the other Euinycetes, 

 develop no mycelium, but con- 

 sist of isolated oval cells which 

 multiply by rapid budding, 

 and only exceptionally become 

 elongated enough to suggest a 

 hypha. The oval vegetative 

 cells contain granular cyto- FlG - 129 ' ~ Saccharomyces cerevisi*. A, active 



plasm, which usually has one fj; b ^ dil ^ < x 1000 >- B ~ D > dividing-cells 



(after WAGER) ; n, nucleus. E, cell contain- 

 er more conspicuous vacuoles . four 8 (After REESS } 



(Fig. 129). A nucleus is prob- 

 ably always present, but it is not readily demonstrated. Under certain condi- 

 tions, as for example when the cells are cultivated upon slices of carrot or 

 potato, the contents of the cells may form (usually) four spores, so that the cell 

 is transformed into a very simple ascus. 



Alcoholic Fermentation. It is from an economic standpoint, how- 

 ever, that the Yeast-fungi are of special interest, as they are the 

 most important agents of alcoholic fermentation. If the cells are 

 placed in a solution of sugar, or a starchy mixture, there soon begins 

 the development of alcohol, with an evolution of C0 2 . It is the 

 escape of the latter in the fermenting dough which causes it to rise. 

 The yeast-cells feed upon the starch and sugar, which are attacked 

 by certain peculiar substances (ferments) excreted by the growing 

 yeast-cells. Of these, diastase converts starch into soluble sugars, 

 and invertase changes cane-sugar into glucose and fructose, which 

 are available to the yeast-cells for food. 



The different species of yeast behave very differently with regard 

 to the fermenting substance, and in making wine and beer the char- 

 acter of the fermented product is largely dependent upon the kind 

 of yeast employed ; hence the importance of regulating this. 



Endomycetaceae The Endomycetaceae comprise a small number 

 of forms differing from the Yeasts in having a true mycelium and 

 usually 4-8-spored asci. In Eremascus the asci arise from the fer- 



