CHAPTER IV 



MANUFACTURE, TRANSPORTATION, AND USE OF 

 FOODS IN PLANTS 



32. The problem of securing food. Plants, 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 simple, and a 

 divided leaf 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 leaves 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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