CYANOPHYCE^;. 215 



280. It was formerly held that the yeast plant was only 

 the immature condition of a mould ;* but Brefeld's re- 

 searches, f which were undertaken to determine whether 

 true yeast ever develops into a filamentous form, appear to be 

 decisive against that view. He found that under different 

 conditions, as with free access of air, or growth in a thin 

 stratum of a neutral solution, the results were always nega- 

 tive, and no filamentous forms appeared. 



(a) Examinations of the yeast plant are easily made by placing a 

 very small drop of active yeast upon a glass slide, and, after covering 

 it in the usual way, keeping it in a warm and moist chamber for some 

 hours, at the end of which time the "budding" will have become 

 quite well marked. A slide so prepared may be examined immedi- 

 ately, but with less satisfactory results. 



(6) Yeast may be grown in abundance by placing a few drops in a 

 quantity of Pasteur's solution, in which it grows with great rapidity 

 in a temperature of 30 to 35 C. (about 90 Fahr.). 



(c) The state in which daughter-cells are formed may be developed 

 by growing the yeast-cells (those called bottom yeast are the most sat- 

 isfactory) upon fresh-cut slices of potato, kohl-rabi, carrot, or, better 

 still, upon small slabs of plaster of Paris. Tlie preparations must be 

 kept moist by covering with a bell-jar ; with proper care the formation 

 of daughter-cells will be seen in a week or ten days from the begin- 

 ning of the experiment. 



(d) In order that the study of these organisms may be at all satisfac- 

 tory the student should be provided with high powers of the micro 

 scope, say from 600 to 800 diameters.:}: 



III. CLASS CYAN-OPHYCE.E. 



281. These are blue-green, verdigris-green, brownish 

 green, or rarely purple or red Protophytes, which, in addi- 

 tion to chlorophyll, contain a soluble coloring-matter 



* "Yeast is, in fact, nothing more than a peculiar condition of a 

 species of Penicillium, which is capable of almost endless propagation 

 without ever bearing perfect fruit." Berkeley's " Introduction to Cryp- 

 togamic Botany," 1857, p. 299. 



f In Flora, 1873. 



| The student is again referred to Huxley and Martin's " Elemen- 

 tary Biology;" in Chap. I. will be found a valuable account of the 

 yeast plant, with directions for making examinations. 



