398 TEXTBOOK OF BOTANY 



10. Immerse a funnel in a battery jar containing an active 

 yeast culture, the upper (small) end of the funnel being just below 

 the surface of the liquid. Insert a test tube filled with the same 

 solution over the open end of the fuimel, so that the open end of 

 the tube is below the surface of the liquid in the jar. If this is 

 carefully done, the tube remains filled with the liquid. Fasten it 

 in this position. Bubbles of gas will rise in the tube and displace 

 the Uquid. When most of the liquid is displaced, turn the tube 

 containing the gas right side up. Light a splinter and insert it 

 into the tube. What happens to the Ught? Why? What is 

 the gas in the tube ? 



11. Place another active yeast culture in a wide-mouthed bottle. 

 Cork the bottle. Through the cork pass a bent tube, one end of 

 which is above the surface of the yeast culture, and the other end 

 of which dips into some lime-water in a tumbler. The gas formed 

 by the yeast will pass into the lime-water. What changes take 

 place in the appearance of the lime-water? Why? 



12. Prepare three jars with molasses solution and yeast. Cover 

 one with dark paper so as to shut out all the hght and keep it be- 

 side your first culture (described in § l). 



13. Place a second in a cool place — in an ice box if one is 

 available. 



14. The third jar should be washed thoroughly in boiling water, 

 and the solution for this jar should be boiled for five minutes after 

 the yeast is added but before placing it in the jar. After the solu- 

 tion is placed in the jar, cover it tightly and place it beside the first 

 culture. 



15. Watch the different cultures and make careful notes of the 

 results, comparing them with the first culture. What do you con- 

 clude as to the following points : 



u.. Does darkness or light afEect the activity of the yeast ? 



b. Does cold affect it ? 



c. What happens to the yeast when it is heated to the boiling point ? 



Compare with bacteria in this respect. 



16. Place some yeast in molasses to which no water has been 

 added. Keep it in, a warm place. Does fermentation take place? 

 Why? 



