CHAPTER V 



THE LEAF AND ITS FUNCTIONS 



The vegetative organs of the plant naturally fall into two 

 groups: The root-system, situated in the soil and concerned 

 primarily with the absorption therefrom of water and certain 

 nutrient materials; and the stem and leaves (together called 

 the shoot), which unfold in the air and are concerned primarily 

 with the manufacture of food, the raw materials for which they 



Fig. 31. — Two types of leaf-venation. At left, notted-veincd leaf of Linden. 

 A, blade. B, petiole. C, stipules. At right, parallel-veined leaf of Solomon's 

 Seal. 



derive from l)oth air and soil. Of the two members of the shoot- 

 system the leaf is the primary and more important one, the stem 

 serving merely to expose the leaves to light and air and to pro- 

 vide a means of conummication between them and the root- 

 system. It is logical, therefore, for us to follow our study of the 

 root with a sliidy of \\\c leaf. 



The Structure of the Leaf. — Before we can understand cleaily 

 the functions which the leaf pei'forms, we shall need to observe 

 with some care its rather complicated structure. 



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