270 TEXT-BOOK OF FUNGI 



Engler and ?&&&, Pflanzenf am ^Exoascaceae, i, i, p. 158 

 (1894). 



Sadebeck, Unters. uber d. Pilzgattung Exoascus, Jahresb. 

 der wissensch. Anst. zu Hamburg, No. i (1883). 



Sadebeck, Die Parasitischen Exoasceen, Jahrb. d. Ham- 

 burg wissensch. Ansf., 10 (1893). 



Saccharomyceteae 



Probably no group of fungi has received more attention 

 than the present, mostly on account of the fermentative 

 power of many species, which render them of great 

 importance from an economic standpoint. The liberation 

 of carbonic acid gas is utilised in the bakery, and the 

 formation of alcohol, a by-product of metabolism, is of 

 equal importance in the brewery. Some wild yeasts cause 

 fermentation on the surface of ripe fruits. 



The yeast-plant is a very simple organism, consisting 

 typically of a single cell. Saccharomyces Ludwigii and 

 some other species sometimes produce a rudimentary form 

 of mycelium. Two modes of reproduction are known : 

 a purely vegetative method known as budding, and a more 

 complicated method by the formation of endospores. A 

 third method is said to occur in some species, where the 

 cell-wall becomes thickened and hardened, practically 

 forming chlamydospores. 



When placed in a nutrient solution at a suitable tem- 

 perature, budding takes place with great rapidity, the 

 solution soon becoming turbid owing to the increase in 

 quantity of yeast-cells. Slight papillae appear at various 

 points on the surface of a cell, these papillae increase in 

 size, and are soon attached to the parent-cell by a narrow 

 neck, and finally fall away, when they soon repeat the 



