YEAST 



31 



Spore-formation. Another mode of reproduction occurs 

 under certain and for the most part unknown conditions. 

 The protoplasm divides within the cellulose membrane, to 

 form two, three, or four compact, rounded spores (Fig. 15). 

 Under favorable conditions these spore capsules burst or sprout, 

 and the spores emerge as ordinary yeast cells which then grow 

 and reproduce by budding. Reproduction by this means is 

 called endogenous sporulation and should be sharply distin- 

 guished from "spore-formation" in bacteria which is solely 

 for protection against drying, etc. 



FIG. 14. Colonies of budding yeast cells. (From Sedgwick and Wilson.) 



Culture Media. The simplicity of structure of yeast cells 

 would naturally suggest a simplification of the vital processes, 

 and lend support to the belief that these might be more readily 

 analyzed than can vital processes in higher types of cells. 

 This belief, indeed, has been realized to a certain extent although 

 the secrets of constructive and destructive metabolism are still 

 unrecognized. The sweet fluids of fruits offer an excellent me- 

 dium in which yeast cells grow and multiply. Even more ex- 



