THE BEAN 



139 



and since it never contains a large proportion of wood, it does not 

 become hard lilie the stems of trees and shrubs. The vascular bundles 

 in the stem branch from time to time, and the branch bundles run out 

 from the stem into the branches and leaves. 



163. Foliage Leaves. — The bean has nothing that cor- 

 responds to the scale leaves of the pine. All the leaves that 

 are formed later than the two seed leaves are foliage leaves, 

 except, of course, the special leaves (sepals, petals, stamens, 

 and pistil) that constitute the flower, and except also some 

 very small green leaves 

 (bracts) borne in the 

 flower clusters. The 

 foliage leaves are alter- 

 nately arranged upon 

 the stem ; that is, only 

 one is borne at any par- 

 ticular level, and no two 

 successive leaves arise 

 from the same side of 

 the stem. The blade 

 of each leaf (Fig. 84) is 

 divided into three leaf- 

 lets, each with a short stalk of its own. Two of the leaflets 

 are attached to the sides of the leaf-stalk, opposite each 

 other ; the third is borne at the end of the leaf -stalk. 



At the point where the leaf -stalk joins the stem or branch, 

 there are two small structures that look like little leaves ; 

 they are called stipules and are really parts of the leaf to 

 whose stalk they are attached. At the base of the stalk of 

 each side leaflet, where it joins the leaf-stalk, there is also 

 an attachment like a stipule but smaller; and at the base 

 of the stalk of the terminal leaflet are two similar attach- 

 ments. 



The blade of each leaflet has a midrib from either side of 

 which pass off branch veins (vascular bundles), some large 



Fig. 83. — Part of a cross section of a leaf 

 (of the lUy) ; a, upper epidermis ; b, layer of 

 closely packed cells ("palisade layer") ; c, a 

 vascular bundle; d, an air-pore. 



