PBOTOPHYTA. 



125 



X74_0 



158. Another family of plants belonging to the Proto- 

 phyta is the Saccharomyces, including the Yeast-plant 

 (Sacoharomyces cerevisice) and other species, 

 which produce fermentation in sugar solutions. 

 The transparent cells are more or less round, 

 oval, or elongated, and multiply by budding 

 (Fig. 235). When the supply of nourishment 

 is less abundant (as when yeast is grown on slices of potato 

 or carrot), the cells are larger, and divide internally into 

 four new cells with cell-walls. These may be called spores ; 

 they escape and grow into cells of the ordinary kind, capa- 

 ble of multiplication by budding. Saccharomyces cerevisice 

 produces the alcholic fermentation ; that is, the sugar in 

 the solution is converted into alpohol with the escape of 

 carbonic dioxide. S. eUipsoides, 8. conglomeratce, and others, 

 live on grapes, and find their way into the juice in the 

 manufacture of wine, and cause the fermentation of the 

 latter. S. myeoderma is found on the surface of spoiled 

 beer or wine; it does not produce fermentation like the 

 others, but putrefaction instead. 



159. Another family of the Protophyta containing (un- 

 like the preceding) chlorophyll is the Nostocs {Nosto- 

 caeecs). The plants consist of rounded cells loosely united 

 into filaments, and imbedded in a jelly-like mass (Fig. 236). 

 At intervals are large, clear cells, called heterocysts, whose 



function is not clearly known. The plants 

 grow in fresh water, or in damp places: 

 They multiply usually by fission of the 

 cells. Filaments sometimes break in pieces 

 capable of motion ; and from these, when 

 at rest, new colonies are formed. The' 



Fig. 235. Yeast- plant (Saccharomyces cerevisiiB). Fig. 2a8. A colony of Nostoc ; 

 the figure on the left moderately magnified ; the one on the right (a single filament) 

 highly magnified. 



