CHAPTER III. THE LEAF. 



27 



tough framework or system of veins, which serves partly for sup- 

 port and partly to conduct the nutritive fluids ; an intervening 



Fig. 54. 



Fig. 55- 



Fig. 56. 



AV^VWV^*^* , ^^V(' 



Fig. 54. — Adnate stipules of Rose. 



Fig. 55. — Stipules of the common Locust converted into spines. 



Fig. 56. — Stipules of Green Briar (Smilax) developed into tendrils. 



soft tissue called the mesophyll, or leaf-parenchyma, and an 

 epidermis which covers the whole. The petiole consists more 

 largely of fibrous tissue, the continuation of the framework of 

 the blade, and possesses comparatively little parenchyma. 



^-^^-w^. The Venation of 



t) V J7W\jTnP7'^ Leaves. By this is 



~ \ \\\ \ v ^. ,N t^ N 0>^ meant the arrangement 



-^~-~'~~"~~" v of the veins or frame- 



Fig. 57. -Pinnule of Osmunda regalis, a Fern, illus- work. In SUch simple 



u-ating furcate venation. leaves as many of the 



Mosses, no veins are present, and the leaf consists merely of a 

 layer of green cells, but in higher plants a venation is always 

 more or less distinctly recognizable. Three different types of it 

 are distinguished, the furcate or forked venation, in which the 

 veins fork or divide once or repeatedly into equal divisions, as 

 seen in many ferns and other cryptogamous plants, but seldom 

 in flowering plants, see Fig. 57 ; the nerved or parallel-veined 



