! LABORATORY AND FIELD EXERCISES 



3. Reproduction by budding. 



a. Do you find yeast plants with two cells joined, namely, 

 one large cell united with a small cell ? Observe a 

 number of these cases of two-celled or three-celled 

 plants. Are the two or three united cells always 

 unlike in size ? Can you determine how these united 

 cells originate from single-celled plants ? 



6. Draw a series of two-celled yeast plants representing 

 differences in size between the constituent cells. 

 Can you now determine the methqjl by which the 

 yeast plant reproduces itself by budding ? How does 

 this method of reproduction differ from that found 

 in Protococcus ? Is it a sexual or a vegetative method 

 of reproduction? 



c. Observe, if possible, wild yeasts in cider or in ferment- 

 ing apples and make drawings to sho\v their struc- 

 ture and mode of reproduction. 



4. Fermentation experiments. Select two flasks of equal size 



and into one pour enough water to cover the bottom. 

 Into the other flask pour an equal amount of actively 

 fermenting yeast solution. 



a. Test both flasks for oxygen and carbon dioxide with a 



flame, with lirnewater, or with bariiun hydroxide. 

 Set aside for an hour, keeping both flasks at a uni- 

 form temperature of 25 C. At the end of an hour 

 test as above for oxygen and carbon dioxide. Result ? 



b. Write up the above experiment in your notes, indicat- 



ing the object, the actual results observed, and your 

 conclusions concerning what was proved with refer- 

 ence to the nature of fermentation by yeast. See 

 account of fermentation in the text. 



c. Fill two fermentation- tubes with yeast solution. Keep 



one at 25 C. and the other at a much lower 



