PLANTS AND THE LIGHT 23 
dandelion should have its leaves as large as the leaves of 
the mullein? Can you prove your conclusion by conditions 
in any materials at hand? Study various vines to see where 
the leaves arise and how they are placed to insure proper 
lighting. Do vines growing on trees and houses differ from 
those growing on the ground? Can you find any vines with 
leaves of two sizes? If so, how are they arranged? Are 
there any procumbent plants that show the rosette habit? 
From these observations do you find any relation neces- 
sarily existing between the size and the number of the 
leaves? Is there any relation between the width of the 
leaves and their number? Between the size of leaves and 
the length of the stem between successive leaves? When 
leaves stand one above another, is there any relation be- 
tween the length of the petiole and the size of the succeed- 
ing leaf? Prove your answers by reference to the speci- 
mens that you have studied. 
LESSON VIII 
Plants and the light—a comparison of shade and sun plants 
Materials.—If the work can be done out of doors, select 
a deeply wooded region, near which is one well exposed 
to light. Locate specimens of cottonwood, wild balsam 
(Impatiens), vines, and various herbaceous plants growing 
in shaded places, also plants of the same species growing in 
exposed places. If the work is to be done in the laboratory, 
specimens of plants from the two regions should be pro- 
vided, or greenhouse material will afford illustrations of 
the two habits. Some distinctly sun-plants, and other dis- 
tinctly shade-plants, may be used even if the same species 
are not represented in both habitats. When good illustra- 
tions are found, it is advisable to make herbarium mounts of 
the leaves for further comparison. In this way a laboratory 
may soon possess a valuable collection for illustration. 
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