LEAVES 



201 



usually present a netted appearance, but in some leaves, 

 such as those of lilies and grasses, they run in somewhat 

 parallel lines. 



When examined under a microscope, each leaf is 

 found to be composed of an almost countless number 

 of cells, which vary in structure and in use. The outer 

 surface, or epidermis, of the leaf is composed of large 

 irregular-shaped cells. The interior of the leaf is filled 

 between the veins with loosely arranged cells forming 

 what is known as the mcsophyll. The epidermis, 



-) Pafisade 

 ssue 



Spongy 

 Tissue 



Chamber 



Fig. 78. Cross section of a leaf of a barberry showing the internal 

 structure, 



although frequently very thin, serves as a protection 

 to the mesophyll, which is easily crushed and dies 

 quickly when the epidermis is removed. In the epi- 

 dermis, on the under surface of the leaf, there are a 

 number of tiny oval openings. These are called 



