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.). 
