186 



CRYPrOGAMS 



■AO: 



Yeast plants: 1 

 and 2 repre- 

 sent sLK-oessive 

 stages in the 

 process of bud- 

 ding. 



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

 are larger than most Bacteria, averaging perhaps 3-2-5-00 

 inch in length. Eacli cell consists of 

 wall and protoplasmic body, generally 

 including refractive grannies 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- 

 cess of "budding." The cell wall is 

 pushed out at some point in a small 

 rounded swelling, which receives pro- 

 toplasmic contents from the parent cell. 

 It increases in size and is tinally cut off 

 Ijy a new cell wall ; though it niay long remain attached 

 to tlie 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, liowever, 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). Jn beer and wine 

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

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

 its bubbles o-ivina: the bread its lifrhtness. 



Bread Mold (Rhizopus) 



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

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

 i)f fine wliite mold will probably make its ai)iieai'ance, 

 unless special precautif>ns have been taken to prcN^ent sucli 

 a result. That the plant may be secni'ed without failure 

 by such means of course demonstrates the iirevalence of 

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

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



