BIOLOGY OF HIGHER SEED PLANTS 59 



of gas given off ? Shade the plant. Do the gas 

 bubbles continue ? Explain, Record the experiment 

 by the usual method. 



b. Can you suggest a method for testing the gas given off 



by Elodea and other water plants when exposed to 

 sunlight ? If so, perform the experiment as you have 

 planned it. 



c. Record object, results, and conclusions in the usual 



manner. 

 4. Gaseous exchanges in land plants. 



a. Place three tubulated bell jars in three large plates or 



pans which will hold water. Narrow-necked bottles 

 (Wolff-neck bottles are good) may be used instead of 

 bell jars. Place in two of the bell jars, or bottles if 

 these are used, vigorous leafy shoots of plants. If bell 

 jars are used, pour water into the plates or pans until 

 it rises an inch or more in each jar. 



b. Lower into each jar or bottle a lighted candle, and cork 



tightly with a rubber cork or a vaselined common 

 cork. How long does the air in the jars support com- 

 bustion ? Why do the candles go out ? How does the 

 burning of the candles change the composition of the 

 air in the jars ? Record answers to points (1) and (2) 

 under d. 



c. Put all of the above jars in sunlight and cover one con- 



taining a leafy plant so as to exclude light. After 

 two or three hours lower lighted candles into each 

 jar and test quickly to see whether the air in them 

 will support combustion. Is there a difference in the 

 air in the jars in this respect? P>e able to explain 

 any differences observed. 



d. Record the experiment in the usual manner. Under 



Results indicate the composition of the air in the 



