366 STRUCTURE AND LIFE HISTORIES 



is recognized that there are numerous groups, and that 

 the members of any one group differ from those in every 

 other group in some fundamental point. By such com- 

 parisons botanists have been able to classify all known 

 plants into more or less clearly defined groups and sub- 

 groups. The larger the number of characters considered, 

 the smaller the group, and vice versa. 



The divisions of the plant kingdom already studied, and 

 their distinguishing characters are as follows : 1 



Divisions of the Plant Kingdom 



1. Thallophytes. Plant body a thallus; no archegonia. 



2. Bryophytes. Archegonia; no vascular system. 



3. Pteridophytes. Vascular system; no seeds. 



These four divisions are, of course, distinguished by 

 other characters than the ones just indicated, but these 

 stand out prominently as positive and negative character- 

 istics of the respective groups. 



These three divisions are further subdivided, as shown 

 on the following page. 



' Adapted from Coulter (J. M.). 



