64 MORPHOLOGY AND CULTUiRE OF MICROORGANISMS 



Summing up the elements of which a yeast cell consists are a cyto- 

 plasm with a chondrium, a nucleus with clearly differentiated structure, 

 vacuoles containing numerous metachromatic corpuscles, a membrane 

 of a nature not yet clearly defined. 



Cytological Phenomena during Multiplication. — During the 

 budding of the yeasts, cytoplasm enters the young bud with some chon- 

 drium; then, when the bud has reached a certain size, the cytoplasm 

 forms in it a httle vacuole in which appear 

 metachromatic corpuscles (Fig. 46, 2-7). 



In the course of these phenomena, the 

 nucleus retains the position which it occupied 

 in the mother cell before the appearance of 

 the bud. Only when the bud is quite large 

 does the nucleus begin to divide. It is elon- 

 gated so that one end penetrates the bud; the 

 nucleus then resembles an elongated dumb- 

 bell with the larger head remaining in the 



Jj(^-J7-—Saccharomyces mother ceU and the other, smaller head, in the 

 elhpsoideus. Young cells , , - , '. _. „s 



with nucleus. bud (Fig. 44, 6, 7 and 8; Fig. 46, 2, 7 ; Fig. 48). 



Soon the part of the dumb-bell which is 

 stretched out breaks near the neck of the bud, forming two nuclei of 

 unequal size, at first tapering spherical in shape, and later rounded 

 off: one is the nucleus of the mother cell and the other that of the 

 bud. This division is therefore effected by the direct method; it is an 

 amitosis. In the Schizosaccharomyces, where the cells do not multiply 

 by budding as in other yeasts, but by a transverse partition, the 

 nuclear division is effected by amitosis: the nucleus, situated in the 

 center of the cell, elongates along the longitudinal axis of the cell and 

 resembles a dumb-beU, ending by dividing in the middle, thus forming 

 two nuclei of the same size. Soon a transverse septum appears be- 

 tween the two nuclei and separates the two daughter cells. 



We have now to note the modifications which arise in the structure 

 of the cells during the different phases of development and at the time 

 of sporulation. 



Variation in the Cellular Structure during Development. — 

 In the course of development, especially during fermentation, yeasts 

 reveal cytological phenomena which render their structure more com- 

 plex and more difficult to interpret. Let us take for example the study 



