236 



PLANT STRUCTUKES 



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. 



