244 LEAVES 



leaf. In some cases there are special strengthening tissues! I 

 developed within the leaf, either in connection with the conduc- 

 tive tissues or separately. Third, most important of all is the 

 food-making tissue, known as the mesophyll, because it fills the 

 interior of the leaf. The green mesophyll is usually called chloren- 

 chyma because of its green color. 



The Conductive Tissues. The conductive tissues of leaves 

 consist of vascular tissues similar to those of the vascular bundles 



FIG. 229. A, leaf of Solomon's Seal, showing parallel veining; B, leaf of 

 Willow, showing net veining. After Ettinghausen. 



of stems and roots. They constitute the veins. The veins are 

 simply branches of the vascular bundles of the leaf trace, and 

 the leaf trace is a branch of the vascular cylinder of the stem. 

 Thus through the direct connection of the vascular tissues of the 

 leaves with those of the stem, which in turn are in direct connection 

 with the vascular tissues of the roots, all parts of the plant are 

 brought into close communication for the exchange of materials. 



