I LABORATORY AND FIELD EXERCISES 



they compare in number and size with the female 

 gametes ? Were the male gametes formed like the 

 females, by cell and nuclear division ? Draw. 

 /. Life history. Write a graphical life history of Fucus 

 similar to that of tipirogyra and Vaucheria. 



B. THE FUNGI 

 YEAST 



1. Composition of compressed yeast. 



a. Method. Remove a small portion of compressed yeast 



to a slide and mount in a drop of water, separating 

 well with needles. Add weak iodine solution and 

 observe with low and high powers of the microscope. 



b. Observation. Do you find indications of the presence of 



starch in yeast cakes ? Can you distinguish the minute 

 yeast plants looking like dots under low power ? Ex- 

 amine these structures with a high power. What is the 

 structure of a yeast plant ? Contrast it with an alga 

 like Protococcus. In what respects are the two plants 

 similar ? In what respects are they different ? Why 

 is the yeast cake not made up from pure yeast plants ? 



c. Make a drawing to indicate the composition of com- 



pressed yeast. 



2. Cellular structure. 



a. Method. Cultivate yeast by adding about 1 g. of com- 

 pressed yeast cake to 15 cc. of a sugar solution made 

 up as follows : to 1 cc. of water add 2 cc. of com m on 

 molasses, or make up a 10-15 per cent sugar solution 

 in water. Keep the sugar solution at about 25-28 C. 

 after adding the yeast in the above proportions. After 

 vigorous growth and fermentation have begun, add a 

 drop of the solution to a glass slide and cover. 



