THE CELL. 43 



A STUDY OF CELLS. 



In the following studies it is designed to illustrate the different 

 forms of cells and the methods of cell-multiplication. Types are 

 presented which are believed to have a special bearing on the work 

 of the histologist. Yeast, Protococcus, and Spirogyra have been 

 selected to illustrate plants, and the Amoeba, Green Euglaena, and 

 Slipper Animalcule, to illustrate animals. 



STUDY OF THE YEAST PLANT. 



The Yeast Plant is a unicellular, chlorophylless saprophyte, which 

 reproduces by budding and ascospores. 

 Classification: 



Kingdom Vegetable. 



Series Cryptogamia. 



Sub-kingdom Thallophyta. 

 Class Fungi. 



Sub-class Ascomycetes. 



Life History and Morphology. The Yeast Plant, Saccharomyces 

 cervisice, is the common species used by brewers and bakers. It con- 

 sists of cells, round or oval in outline. Each plant, or cell, is called 

 a torula; when the cell produces spores the term gonidia, or asco- 

 spores, is applied to them, while the term ascus is applied to the 

 cell. The cell-wall is transparent and composed of cellulose. The 

 protoplasm contains one or more clear spots (vacuoles), and is be- 

 lieved to contain a nucleus. Multiplication occurs by budding. A 

 spherical projection, or papilla, is produced on the wall of the parent 

 cell, which forms for itself a cell-wall, and, eventually, by a parti- 

 tion, becomes separated and assumes an independent existence. Be- 

 fore separation occurs, however, owing to rapid growth, the daugh- 

 ter cells often throw out buds, thus forming a colony or chain. Ee- 

 production also occurs by the formation of endospores. The proto- 

 plasm of the parent cell divides into four masses, each of which 

 forms a new cell-wall. These are called ascospores and have the 

 power to perpetuate the plant under unfavorable conditions. By 

 the dissolution of the wall of the parent cell the ascospores are set 

 free and, under favorable conditions, reproduce the plant. 



In size, the yeast plant ranges from T(T Vir to *iW inc ^ * n diame- 



