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. 
* If the taper 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? 
