30 



PROTOPLASM AND THE CELL 



All of these constituents of the cell vary according to conditions. 

 In old cells the cellulose membrane is thicker than in young 

 cells, as can be easily demonstrated by the use of aqueous solu- 

 tion of magenta. The nucleus is larger and more conspicuous 

 in large cells and may be found in the process of division (Fig. 

 13). Fat droplets and vacuoles, also, vary in number and size 

 according to the conditions. 



FIG. 13. Yeast cells showing nuclei and successive stages in the process of 



budding. (From Sedgvvick and Wilson.) 



REPRODUCTION 



Budding. In active, growing yeast it is very easy to find 

 cells in the process of reproduction. This is brought about by 

 budding or gemmation, which begins with a local swelling usu- 

 ally at one pole of the spheroidal cell. The membrane appears 

 to give way or to weaken at one point, and the inner protoplasm 

 presses into this region, forcing out the thinned membrane, until 

 a well-marked bud is formed. Later this bud is constricted off 

 and it becomes a separate, young, yeast cell. Frequently the 

 bud continues to grow until mature without breaking away from 



