. Foundations of botany. eor less granular semi-fluid proto-plasm, sometimes containing aportion of clearer liquid, the vacu-ole, well shown in the larger cellsof Fig. 323. Substances which compose the Yeast-Cell. — The cell-wall iscomposed mostly of cellulose; the protoplasm consists largely ofwater, together with considerable portions of a proteid substance,^ 1 This is not the ordinary commercial yeast. 2 It may be found troublesome to apply tests to the yeast-cell on the slide,under the cover-glass. Testing a yeast cake is not of much value, unless itmay be assumed that compressed yea
. Foundations of botany. eor less granular semi-fluid proto-plasm, sometimes containing aportion of clearer liquid, the vacu-ole, well shown in the larger cellsof Fig. 323. Substances which compose the Yeast-Cell. — The cell-wall iscomposed mostly of cellulose; the protoplasm consists largely ofwater, together with considerable portions of a proteid substance,^ 1 This is not the ordinary commercial yeast. 2 It may be found troublesome to apply tests to the yeast-cell on the slide,under the cover-glass. Testing a yeast cake is not of much value, unless itmay be assumed that compressed yeast contains little foreign matter and con-sists mostly of yeast-cells. Still the test is worth making. Millons reagentdoes not work well, but the red or maroon color which constitutes a good testfor proteids is readily obtained by mixing a teaspoonful of granulated sugarwith enough strong sulphuric acid to barely moisten the sugar throughout,and then, as quickly as possible, mixing a bit of yeast cake with the acid and. Fig. 197. — Yeast (Saccharomycts ellip-soid eus) budding actively. A, a single cell; B, group of two buddingcells ; C, a large group ; b, buds. TYPES OF CRYPTOGAMS; THALLOPHYTES 269 some fat, and very minute portions of sulphur, phosphorus, potash,magnesia, and lime. It is destitute of chlorophyll, as would beinferred from its lack of green color, and contains no starch. 324. Food of the Yeast-Cell; Fermentation. — The diluted molassesin which the yeast was grown in Exp. XXXIX contained all themineral substances mentioned in Sect. 323, together with sugar,proteid materials, and water. The addition of a little nitrate ofammonium would probably have aided the growth of the yeast inthis experiment, by supplying more abundantly the elements outof which the yeast constructs its proteid cell-contents. A great dealof sugar disappears during the growth of the yeast.^ Most of thesugar destroyed is changed into carbon dioxide (which the studentsaw rising through the
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