CHAPTER TIT 
FOLIAGE LEAVES: FUNCTION, STRUCTURE, AND PROTEC- 
TION 
A. Functions of foliage leaves 
24. Functions in general. AVe have observed that foliage 
leaves are light-related organs, and that this relation is an 
important one is evident from the various kinds of adjust- 
ment used to secure it. AVe infer, therefore,, that for some 
important function of these leaves light is necessary. It 
would be hasty to suppose that light is necessary for every 
kind of work done by a foliage leaf, for some forms of work 
might be carried on by the leaf that light neither helps nor 
hinders. Foliage leaves are not confined to one function, 
but are concerned in a variety of processes, all of which 
have to do with the great work of nutrition. Among the 
variety of functions which belong to foliage leaves some of 
the most important may be selected for mention. It will 
be possible to do little more than indicate these functions 
until the plant with all its organs is considered, but some 
evidence can be obtained that various processes are taking 
place in the foliage leaf. 
25. Photosynthesis. The most important function of the 
foliage leaf may be detected by a simple experiment. If 
an active leaf or a water plant be submerged in water in a 
glass vessel, and exposed to the light, bubbles may be seen 
coming from the leaf surface and rising through the water 
(see Fig. 23). The water is merely a device by which the 
bubbles of gas may be seen. If the leaf is very active the 
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