186 CRYPTOGAMS 



sizes (Fig. 302). Though very small plants, the Yeasts 

 are larger than most Bacteria, averaging perhaps ^o}iOQ 

 inch in length. Each cell consists of 

 wall and protoplasmic body, generally 

 including refractive granules and a 

 large sap cavity. 



Reproduction. — New individuals are 

 formed not by division into two equal 

 parts, as in the Bacteria, but by a pro- 



302. Yeast plants: 1 ^ess of "budding." The Cell wall is 



and 2 repre- pushed out at some poiut in a small 



sent successive t i ii. i,* i 



stages in the I'ounded swelling, which receives pro- 

 process of bud- toplasmic contents from the parent cell. 

 ^^^' It increases in size and is finally cut off 



by a new cell wall ; though it may long remain attached 

 to the parent cell. Before its separation it may itself bud 

 in one or more directions, and thus irregular colonial 

 growths arise. Yeasts may multiply very rapidly, an 

 entire new generation appearing in a couple of hours. 



There are many different sorts of Yeast. The usefulness 

 of all Yeasts, however, depends upon their power of 

 decomposing certain sugars, with the resultant formation 

 of alcohol and carbonic acid gas (that is, their power of 

 exciting alcoholic fermentation). In beer and wine 

 making, alcohol is the product sought ; in bread raising, 

 on the contrary, carbonic acid gas is the useful product, 

 its bubbles giving the bread its lightness. 



Bread Mold (Rhizopus) 



445. If fresh moist bread is placed in a tightly closed 

 dish in a warm place, within a few days a thick growth 

 of fine white mold will probably make its appearance, 

 unless special precautions have been taken to prevent such 

 a result. That the plant may be secured mthout failure 

 by such means of course demonstrates the prevalence of 

 its minute spores in the air, or in the dust which has 

 settled on the bread or on the dishes used. If we were to 



