104 THE VEGETATIVE FUNCTIONS OF PLANTS 



106. Consumption of Oxygen Demonstrated. The 



exchange of gases between the atmosphere and the 

 interior of the plant may readily be demonstrated by a 

 simple experiment, as follows. Into each of seven glass 

 cylinders (Fig. 68) fit a partition of wire gauze, so as to 

 divide the space vertically into equal parts. Into the 

 first jar place nothing, and fill the space, on one side only 

 of the wire gauze, in each of the other six jars respectively, 

 with germinating seeds (pea or lupine), living herbaceous 

 stems, living roots (washed free from soil but moist and 

 fresh), green leaves, freshly opening flower buds, and 

 (in the last jar) fresh mushrooms or other fleshy fungi. 

 Test the air in the empty half of each jar with a lighted 

 taper to make sure that it contains sufficient oxygen to 

 support combustion, and then seal all the jars air-tight 

 with rubber stoppers, and set them side by side in any 

 convenient place except in direct sunlight. 1 At the end 

 of 1 2 to 24 hours again test the air in each of the jars with 

 the lighted taper. The air in the first jar, containing no 

 plant material, will still support combustion, but the 

 taper will be extinguished at once when lowered into each 

 of the other six jars. 2 This shows that the air in each of 

 these jars has become poorer in oxygen, and that it does 

 not now contain enough to support combustion. 3 This 



1 The heat of direct sunlight is unfavorable to the best results. 



8 If the iaper is not extinguished in the jar containing the green leaves, 

 the student should be able, from his knowledge of other plant processes, 

 to suggest a probable reason why, and to devise suitable modifications of 

 the experiment so as to demonstrate the respiration of green leaves. In 

 this and other tests of the air, the cork stopper should not be removed any 

 longer than is absolutely necessary, and the lighted taper should be lowered 

 and removed quickly. 



3 Does the experiment show that there is no oxygen in the jars in which 

 the flame is extinguished? 



