MORPHOLOGY AND RELATIONSHIPS OF MICROORGANISMS 39 



yeast cell are more highly differentiated than are those of bacteria. 

 The ectoplast, or limiting membrane of the protoplasm, is easily 

 demonstrated by plasmolyzing the cell. This ectoplast (German 

 Hautschicht) is the only membrane of the young cell, and the 

 cell wall is probably secreted by it. The protoplasm is differ- 

 entiated definitely into a nucleus and cytoplasm. The nucleus 

 is not as easily demonstrated as in the higher plants and animals,- 



Fig: 19. Diagram of budding yeast cells and their contents: a, Glycogen 

 granules; b, vacuoles; c, nucleus; d, dividing nucleus in bud formation. 



but may be shown by proper staining methods. The cytoplasm 

 usually contains one or more vacuoles, spaces filled with cell sap 

 and not taking the stain as does the cytoplasm. Older cells 

 may also show oil globules or glycogen granules. 



Reproduction in Yeasts. Yeasts commonly multiply vege- 

 tatively by budding. A bit of the protoplasm protrudes on one 

 side of the mother cell, the nucleus divides, and one part goes to 



Fig. 20. Spores (ascospores) of the yeast (Hansen). 



the bud, the other remains within the cell, the bud enlarges, 

 develops a cell wall, and is constricted off as a distinct individual. 

 Many yeasts may also under favorable conditions produce spores. 

 The development of the spores in the yeast cell differs considerably 

 from that in the bacteria. The latter typically have but one spore 

 developed within the cell, while a yeast cell usually produces two, 

 four, six, or even eight spores. The nucleus divides several times 

 to form a number of nuclei, each of which, together w r ith the 



