MORPHOLOGY OF HIGHER PLANTS. 



369 



Dicotyledons resembles very closely that of the Monocotyledons, 

 except that in the latter the palisade-cells often radiate towards 

 the center of the mestome-strands. There are, however, many 

 instances of a similar development in the leaves of Dicotyledons. 

 Abnormal structures are common in leaves, especially in such 



FlG. 215. Transverse section of leaf of Phytolacca decandra showing upper epidermis 

 (ue), palisade cells (p), raphides (r), spiral tracheae (v), loose mesophyll (m) with large 

 intercellular spaces, and lower epidermis (le) with a stoma. 



as are not held in a horizontal position, but vertical, as those of 

 Eucalyptus, the Irideae, etc. 



The Epidermis forms the surface of the leaf and may con- 

 sist of one or more layers of cells. The outer walls are cutinized, 

 and when nearly smooth the leaf is said to be GLABROUS. They 

 may be covered or whitened with a bloom, as in magnolia, when 



2 4 



