CHAPTER III 
PLANTS AND THE LIGHT 
As much as possible of the work outlined in this chapter 
should be done in the field. If field-work can not be done, 
abundance of material should be carried into the laboratory. 
Although chlorophyll must be exposed to sunlight, it 
does not follow that all plants have similar structures bear- 
ing chlorophyll, nor that they expose it to the light in the 
same way. The most common plants have leaves, which 
are structures specialized for chlorophyll work. It is evi- 
dent that if a given plant has a number of leaves, there 
must be some definite arrangement among them, otherwise 
some might interfere with the work of others. If one leaf 
lies directly upon another, the lower one will not have light 
enough to enable it to work well. Plants show various de- 
vices for securing a large extent of chlorophyll exposure 
and for preventing continuous shading of some of the leaves. 
It must be borne in mind, as will be seen in later lessons, 
that while leaves are arranged with reference to the light, 
the best conditions for proper air and temperature must 
also be secured, and what would fully meet one condition 
might not always be suitable for others. 
LESSON V 
Leaves and the light—on upright stems 
Materials.—Such plants as geranium, milkweed, sun- 
flower, horse-ragweed, and branches of horse-chestnut, oak, 
maple, elm, etc. 
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