116 REPRESENTATIVE PLANTS 



size and shape of the yeast cells (really one-celled plants). 

 Do you find chlorophyll ? (The lower forms of plants lack- 

 ing this green color are called fungi.) Observe a large 

 round mark in the cell, a vacuole or vescicle, and surround- 

 ing this a more or less granular cytoplasm (all the cell 

 features ordinarily visible). 



Effect of iodine. Mixed with the yeast are larger, more 

 irregular cells, with lines on the surface (starch cells). Add 

 dilute iodine, and observe the result to the yeast and starch 

 cells. Examine for cells of different sizes and cells of 

 various sizes placed end to end (as in a chain). This is re- 

 production by budding. 



Caution. Do not mistake accidental contact for real chains. 



Drawings. Draw yeast and starch cells and yeast chains, 

 scale of ^ in. for smaller cells. 



Bread and yeast. Study bread making in the books, and 

 explain the part that yeast plays in this operation. What 

 effect has baking the bread on the yeast plants ? In what 

 great industries does yeast have an important share ? In 

 what ways may yeasts be injurious or harmful to man ? 

 How may their presence or growth be prevented ? Consult 

 the subject of fermentation. 



Experiments and problems. Place a small and equal por- 

 tion of a compressed yeast cake in each of four bottles, viz. : 



1. Filled with distilled water. 



2. Filled with Sach's nutritive solution (for green plants, 

 consult reference books for formula). 



3. Filled with distilled water to which a little starch is 

 added. 



4. Filled with distilled water to which a little sugar is 

 added. 



Observe the results. What does this show regarding the 

 food of this fungus ? How would you explain the discov- 

 ery of the first yeast preparation ? What are " wild yeasts " ? 



