228 ELEMENTS OP BOTANY. 



been placed in a slender test-tube and held for two or three minutes in a 

 cup of boiling water. 



With a very small cover-glass, not more than f inch in diameter, it 

 may be found possible by laying a few bits of blotting-paper or card- 

 board on the cover-glass and pressing it against the slide to burst some of 

 the stained cells and thus show their thin, colorless cell walls and their 

 semi-fluid contents, protoplasm, nearly colorless in its natural condition 

 but now stained by the iodine. 



278. Experiment 33. Can Teast grow in Pure Water or in 

 Pure Syrup ? — Put a bit of compressed yeast of about the size of a grain 

 of wheat in about four fluid-ounces of distilled water, and another bit of 

 about the same size in four fluid-ounces of 10-per-cent solution of rock 

 candy in distilled water ; place both preparations in a warm place, allow 

 to remain for 24 hours and examine for evidence of the growth of the 

 yeast added to each. 



I II 



Fig. 198. — Two Species of Yeast, increasing by Budding. (Greatly magnified.) 

 I, a species -with the buds very numerous and well defined. II, the common 

 species. 



279. Size, Form, and Structure of the Yeast Cell. — The student has 

 discovered by his own observations with the microscope that the yeast 

 cell is a very minute object, — much smaller than most of the vegetable 

 cells which he has hitherto examined. The average diameter of a yeast 

 cell is about j^'^^ of an inch, hut they vary greatly both ways from the 

 average size. (Measure an average cell in Fig. 198, II, and calculate 

 about how many diameters magnifying power were used for that 

 flgure.) 



The general form of most of the cells of ordinary yeast is somewhat 

 egg-shaped. The structure is extremely simple, consisting of a thin cell 

 wall, which is wholly destitute of markings, and a more or less granular 

 semi-fluid protoplasm, sometimes containing a portion of clearer liquid, 

 the vacuole, well shown in the larger cells of Fig. 198, I. 



