CHAPTER IV 
MANUFACTURE, TRANSPORTATION, AND USE OF 
FOODS IN PLANTS 
32. The problem of securing food. Piants, like animals, can- 
not continue to live and grow without nourishment, but like 
animals, they may secure the needed nourishment in a variety 
of ways. Reference has already been made to some of the ways 
in which roots, stems, and leaves are related to the plant’s food 
supply, but we shall need to consider further the machinery 
and processes by means of which green plants manufacture 
the things that nourish them. 
33. Structure of a leaf; epidermis. In Chapter II the gen- 
eral form of the leaf and some of its functions were discussed. 
A more detailed study of leaf structure and function is neces- 
sary for the discussions of the present chapter. 
Most leaves consist of the petiole, or leafstalk, and the blade, 
or expanded portion. In some leaves there is no petiole; 
that is, the leaf is sessile, or rests directly upon the stem or 
branch that bears it. In some leaves the blade is divided into 
several parts, or leaflets. An undivided leaf is s¢mple, and a 
divided leat is compound. Leaves vary in size, from those 
that are so small that they are not readily visible, to those so 
large that they are several feet in width or several yards in 
length. In color most leaves are green, but they differ in 
strength of color, and a careful observation usually discloses 
a difference in greenness between the two leaf surfaces, or 
between different parts of the same surface. It is possible to 
observe within most Jeaves the more or less regularly arranged 
veins, or fibrovascular bundles, which are not green. Also on 
one or both leaf surfaces, as in the mullein, begonia, and thistle, 
there often develop outgrowths known as hairs. 
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