THE WALLFLOWER 69 



tissue is called the palisade parenchyma. Its cells are 

 cylindrical in form, and have narrow intercellular 

 spaces between them. 



The lower half of the mesophyll, on the other hand, 



U.S. 



FIG. 26. Part of a transverse section of a leaf of the Wall- 

 flower, e, epidermis ; cu, cuticle ; p.p, palisade paren- 

 chyma ; s.p, spongy parenchyma ; s, stoma ; h, hair ; U.S., 

 upper, L.S., lower, surface of leaf. Magnified 165. (R. S.) 



consists of very loosely arranged irregular cells, with 

 very large air spaces between them. These cells, like 

 those of the palisade parenchyma, contain chlorophyll- 



