. A text-book of botany for secondary schools. Botany. 138 A TEXT-BOOK OP BOTANY. sence of tubercles on the roots of leguminous plants or by the failure of such plants to grow at all. 78. Yeasts.—Yeasts are one-celled plants that reproduce by budding. This curious method consists in a cell's putting out one or more projections which gradually enlarge and finally become pinched off. Often the cells thus pro- duced cling together in short irregu- lar chains (Fig. 124). The chief in- terest in connection with yeasts is the important part they play in the fermentation of sugar solutions, " sp
. A text-book of botany for secondary schools. Botany. 138 A TEXT-BOOK OP BOTANY. sence of tubercles on the roots of leguminous plants or by the failure of such plants to grow at all. 78. Yeasts.—Yeasts are one-celled plants that reproduce by budding. This curious method consists in a cell's putting out one or more projections which gradually enlarge and finally become pinched off. Often the cells thus pro- duced cling together in short irregu- lar chains (Fig. 124). The chief in- terest in connection with yeasts is the important part they play in the fermentation of sugar solutions, " split- ting" the sugar into alcohol and car- bon dioxide, a process also induced by certain bacteria (§ 77), but chiefly by the yeasts. Fermentation by yeasts is employed on a large scale in the manufacture of beer, wine, and spirits, and in the making of bread. In the last-named process, the dough is inoculated with yeast plants and placed in a sufficiently warm temperature to induce rapid growth. The plants begin to reproduce act- ively by budding; the sugar in the dough is split into alcohol and carbon dioxide; and the latter, being a gas, ex- pands and puffs up the dough, making it light and porous, that is, causing it to "; The yeasts commonly used have been cultivated for centuries and are not known in the wild state. There are also "wild yeasts" of many kinds, and many spores of the higher Fungi behave like the yeasts in budding and induc- ing fermentation. The " working " of yeast may be demon- strated by introducing some of the yeast preparations into a solution of sugar or sirup and setting it in a warm place. After a few hours the bubbles of carbon dioxide should be seen rising through the liquid. Fig. 124.—Yeast-cells, re- producing by budding, and forming Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these i
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