LEAVES 77 



cLyma cells and the tracheary tissues are reduced to spirally and 

 reticularly thickened tracheids. Thev serve to carry water, sugar 

 and other compounds to and from the leaves, as will be explained 

 later (see Chapter XVIII). The primary cortex is represented 

 by the palisade and mesophyll cells (Fig. 59). The palisade 



Fig. 58. — Ivy leaves on a wall showing the arrangemelit'with very little overlapping. 



cells are more or lees cylindrical, very compact and are found 

 just beneath the upper' epidermis. They are placed at right 

 angles to the surface. The mesophyll lies between the palisade 

 and the lower epidermis and consists of irregularly shaped cells 

 with numerous- intercellular spaces. The palisade and m.eso- 

 phyll cells are parenchyma tissue and are rich in protoplasm. 



