148 PRACTICAL BOTANY. 



The Saccharomyces, or Yeast Plants, are by some authori- 

 ties classed with the Bacteria. Their proper place in the 

 scheme of classification has not been determined. The 

 formation of ascospores under certain conditions of ex- 

 istence, and their resemblance in other respects to the 

 Ascomycetes, are strong reasons for placing them in this 

 class. 



The yeast cell is ovoidal in shape. It consists of a 

 very delicate transparent wall of cellulose, inclosing proto- 

 plasm. More or less distinct, noncontractile vacuoles 

 may be seen. The vacuoles are simply spaces in the 

 interior of the cell not filled by the protoplasm. They 

 are, of course, filled with fluid. In some cells highly 

 refractive particles of fat and other granules, which are 

 the result of the nutritive processes of metabolism, are 

 found. The nucleus can be seen only after the use of 

 special staining processes which have been discovered 

 recently. 



YEAST. PRACTICAL STUDIES. 



Dissolve a yeast cake in water to which some sugar has 

 been added, or better in Pasteur's solution. After it has 

 been growing for some hours, place a drop of the fluid on 

 a glass slip and cover lightly with a cover glass. Examine 

 with high power. 



1. Observe the prevailing ovoidal shape of the highly 

 transparent cells, being careful not to confound starch 

 granules that may be present with the yeast cells. If the 

 yeast is in an actively growing condition, the character- 

 istic mode of reproduction by budding will be seen. Bud- 

 ding is a modification of cell division in which one of the 

 newly formed parts is smaller than the other. The small 

 bud rapidly grows to the full size of the mother cell and 

 separates from it. The plant is, therefore, unicellular, 

 though retardation in the separation of the daughter cells, 



