MORPHOLOGY OF HIGHER PLANTS. 365 



THE INNER STRUCTURE' OF THE LEAF 



In all green leaves the typical structure is as follows : A cuticle 

 covers the outer cell-wall of the epidermis, while the epidermis 

 itself shows much of the same modifications as exist in the stem ; 

 frequently the lumen of the cells of the epidermis is wider on the 



FIG. 210. Group of transplanted wild plants showing variation in form of leaves. 

 A, Cinnamon fern (Osmunda cinnamomea) showing sporophylls (fertile leaves) and a cluster 

 of pinnatifid sterile leaves, the pinnae being linear-lanceolate and deeply pinnatifid; B, 

 wild ginger (Asarum canadense) showing basal, reniform, long-petiolate leaves with cordate 

 base and slightly pointed apex; C, young hickory (Hicoria ovata) showing the odd-pinnate 

 (impiri pinnate), 5- to 7-foliate leaves; D, ternate, decompound leaf of Virginia grape fern 

 (Botrychium virginianum) ; E, digitately compound leaves of cinquefoil (Potentilla). 



ventral face than on the dorsal. Hairs abound on the leaves in 

 many plants, and stomata are especially frequent on the dorsal 

 surface. The upper epidermis may further be characterized by 

 the presence of water-pores, the origin and function of which have 

 already been described (Fig. 147). 



