26 



General Botany 



The epidermis and the stomata. 



flat (Fig. 14), irregularly shaped, 



The cells of the epidermis are 

 closely united, and in most 



Figs. 14 and 15. Upper and lower epidermis of leaf of common periwinkle (Vinca). Lobed, 

 interlocking epidermal cells are strikingly different from the regular type shown on the 

 preceding page. 



plants colorless. The cell walls on the side of the epidermis 

 which is exposed to the air become thickened with a wax-like 

 material called cutin, which forms a layer over the surface of the 

 leaf. This layer is called the cuticle. It is useful to the plant 

 because water does not pass through it readily, and it reduces 

 the amount of water that would otherwise evaporate from the 

 epidermal cells. It may be compared to the enamel covering of 



A 



Fig. I 



6. Illustrating terms used in describing the shapes of leaves : A, linear ; B, lanceolate ; 

 C, spatulate ; D, ovate ; E, obovate ; F, oblong ; G, cordate ; H, peltate. 



