MORPHOLOGY OF HIGHER PLANTS. 371 



portant in distinguishing plants that resemble 'each other. The 

 size and number of stomata as well as their distribution and 

 arrangement with respect to each other varies in different plants. 

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

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

 ent are quite functionless. Sometimes the stomata are depressed 



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

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

 'Coni ferae. 



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

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



