EXERCISE 78 

 STRUCTURE OF YEAST 



Materials. Fresh cake of compressed yeast and one of the cul- 

 tures from preceding exercise ; microscopes ; slides and covers. 



Directions for work. Rub the fresh surface of the yeast cake 

 lightly across the slide. Add a drop of water and cover glass. 

 Examine with a microscope. The small objects seen are yeast 

 plants and starch grains. If you cannot distinguish one from 

 the other, add a bit of iodine solution, which will enable you 

 to distinguish the starch. (How?) When you are sure you 

 can recognize the yeast plants, prepare another slide without 

 iodine. In your notes tell what you have learned about the 

 shape, relative size, color, and structure of the yeast plants. 



Prepare another slide from the scum on one of the cultures 

 of yeast in molasses solution. This yeast you know to be in 

 'active condition (Exercise 77). Find out, by examining it, 

 the method by which the number of yeast plants increases. 

 Describe the growth and reproduction of yeast. 



References 



BERGEN and CALDWELL. Practical Botany, pp. 232, 233. 

 BERGEN and CALDWELL. Introduction to Botany, pp. 246, 247. 



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