. The essentials of botany. Botany. PROTOPHTTA. HI and larger, and finally a cell-wall forms between the two, which sooner or later separate from one another (a and b, Fig. 4:1). Under certain circumstances new plants form internally, as in c and d, Fig. 47. 228. Yeast-plants are saprophytes, and live upon the starch of flour. They break up the starch, and in the process lib- erate considerable quantities of carbon dioxide, which appears as bubbles upon the surface of the yeast. Another result of the breaking up of the starch is ^"*- 47.—Yeast-piants in various ° '^ stages of growth, a an
. The essentials of botany. Botany. PROTOPHTTA. HI and larger, and finally a cell-wall forms between the two, which sooner or later separate from one another (a and b, Fig. 4:1). Under certain circumstances new plants form internally, as in c and d, Fig. 47. 228. Yeast-plants are saprophytes, and live upon the starch of flour. They break up the starch, and in the process lib- erate considerable quantities of carbon dioxide, which appears as bubbles upon the surface of the yeast. Another result of the breaking up of the starch is ^"*- 47.—Yeast-piants in various ° '^ stages of growth, a and 6. At c the formation of alcohol: hence ?°'^ ** new ceils have formed by ' "'="'^"= internal cell-formation, a and 6 the growth of yeast-plants in a ^^um^. ^' ' *"** ^ mag^ifled starchy substance is always ac- companied by what is known as alcoholic fermentation. The housewife and baker use yeast-plants for the carbon- dioxide gas which they evolve, to give lightness to the bread, while the brewer and distiller use the same plants for the alcohol produced by their activity. Yeast-plants are now considered to be greatly reduced Sac-fungi (p. 175). Practical Studies.—(a) Fill a strong bottle half full of active yeast, cork tightly, and keep for au hour or two in a warm room. Draw the cork and notice the violent escape of gas (carbon dioxide). (S) Place a small drop of the j'east upon a glass slide, add a little water, cover with a cover-glass, tapping it down gently. After a little examination under a high power of the microscope, add iodine, which will stain the starch-grains blue or purple, and tlie yeast-plants yellowish. Many of the latter will be found in process of budding, as in a and b, Fig. 47. (c) Spread a half-teaspoonful of yeast on a fresh-cut slice of potato or carrot; cover with a tumbler or bell-jar to keep it moist; after a few days (4 to 8) examine for cells which are reproducing by internal cell-formation, as in e and d, Fig. Pl
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