236 



PLANT STRUCTURES 



It is the combination of characters which determines a 

 group. 



MONOCOTYLEDONS 



130. Introductory. This great group gives evidence of 

 several distinct lines of development, distinguished by what 

 may be called the working out of different ideas. In this 

 way numerous families have resulted that is, groups of 



FIG. 219. A leaf of honey locust, to show twice pinnate branching (bipinnate leaf ). 



CALDWELL. 



forms which seem to belong together on account of similar 

 structures. This similarity of structure is taken to mean 

 relationship. A family, therefore, is made up of a group 

 of nearly related forms. Opinions may differ as to what 

 forms are so nearly related that they deserve to consti- 

 tute a distinct family. A single family of some botanists 

 may be " split up " into two or more families by others. 

 Despite this diversity of opinion, most of the families are 

 fairly well recognized. 



