LEAVES 



45 

 A thick 



than when growing where there is ample water 

 cuticle is a good drought-resistant character. 



The epidermal cells do not form a continuous layer over 

 the two leaf surfaces. There are numerous pores or open- 

 ings, the stomata (singular stoma, a mouth) (Fig. 20) . Each 

 stoma is bounded by two modified epidermal cells, differing 



^al^asd 



Fig. 20. — Diagram showing the structure of a representative leaf. 

 (After Stevens.) 



from ordinary epidermal cells in form, in their abihty to 

 change shape, and in the possession of chloroplastids. These 

 are the guard cells. 



Leaves possess many different kinds of surface peculiarities, 

 such as hairs, scales, wax and resin deposits. These are 

 features which tend to retard water loss from the leaf surface. 



There is the widest variation in leaf structure. That 



