244. LEAVES 
leaf. In some cases there are special strengthening tissues 
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 
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Fie. 229. — A, leaf of Solomon’s Seal, showing parallel veining; B, lcaf 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. 
