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LEAVES AND THEIR MODIFICATIONS. 55 
What is the source of the oxygen supply in water 
and in land forms ? 
Photosynthesis consists in the formation of carbohy- 
drate (CH,O) food from water (H,O) and carbon- 
dioxide (CO,) by chloroplasts (chlorophyl bodies) 
in the presence of light. 
How can it be proved that oxygen is liberated dur- 
ing photosynthesis work ? 
Experiment 13. 
How can it be proved that CO, is necessary for 
photosynthesis work ? 
Experiment 4. 
What is the evidence of visible carbohydrate food 
(starch) production ? 
Experiments 13 and 5. 
How can it be proved that light is necessary ? 
Experiment 18. 
How is leaf arrangement associated with light 
relation ? 
In the light relation of leaves, what is the purpose 
of the petiole, and how is it modified ? 
In water plants, why do the leaves which are above 
and below the surface of the water differ so much 
in form ? 
What is the purpose of leaf reduction in the cactus ? 
Where is photosynthesis performed in the cactus ? 
What is the meaning of the thickened leaves in the 
century and cabbage plants ? 
Why do some plants have leaves in the form of 
pitchers and “fly traps” ? 
