MORPHOLOGY OF HIGHER PLANTS. 371 



portant in distinguishing plants that resemble eacli other. The 

 size and number of stomata as well as their distri1)ution and 

 arrangement with respect to each other varies in different plants. 

 For example, in certain saprophytic or submerged plants the num- 

 ber of stornata is greatly or even completely reduced, and when pres- 

 ent are quite f unctionless. Sometimes the stomata are depressed 



Fig. 217. Transverse section of leaf of Matico near two veins; showing the upper 

 epidermis of several layers (e), two layers of palisade cells (p), tracheae (t). sieve (s). collen- 

 chyma (c), loose parenchyma containing crystals of calcium oxalate (ca), and non-glandular 

 hairs (h). 



below the surface of the leaf, this being true in plants occurring 

 in dry or cold districts, and is distinctly characteristic of nianv 

 Coni ferae. 



There is a marked difference in the arrangement of the jiali- 

 sade tissues, the following types being distinguished : i. In bifacial 



