The Leaves. 81 



Section YIII. The Leaves 



We have seen that one or more leaves are normally 

 formed at each node of the stem (116). 



121. The Function of Leaves is food preparation (59). 

 Since food is prepared only in the light, the cells of 

 leaves are in most plants so arranged as to best expose 

 them to light, i. e., in thin, more or less horizontal plates, 

 "which are strengthened and at the same time supplied 

 with water by a network of vascular bundles (68) con- 

 necting with the stem. They are protected by the epi- 

 dermis (65), but have access to air through the stomata 

 (66). 



Each leaf, like the stem and root, is developed from 

 one or more growing points (67), one of which forms the 

 terminus of each lobe or division of the leaf. Cell divis- 

 ion in the leaf is confined to the near vicinity of the 

 growing points, hence an inj ary to the older part of the 

 leaf is not repaired further than by the formation of 

 callus (73) over the wounded parts. 



122. The Cultivator Should Provide for Normal Leaf De- 

 velopment. Since the protoplasm of the plant is nour- 

 ished by pi-epared food (59), and since food preparation 

 in most plants takes place almost wholly in the leaves 

 (121), it is of first importance that the plant be so cared 

 for as to promote normal leaf development. Without 

 this, good crops are impossible. The plants must be 

 grown far enough apart so as not to unduly shade each 

 other; insects and fungi must not be permitted to prey 

 upon them when it is possible to prevent it; and the 

 leaves must not be needlessly removed or injured. 



