CHAPTER III 

 THE LOWER PLANTS 



IN endeavoring to trace the pedigree of the vege- 

 table kingdom, we can rely on the record of 

 the past only to a limited extent. While many 

 plants have left perfectly recognizable fossil re- 

 mains, the record is extremely fragmentary. This is 

 especially true of the delicate and more perishable 

 plants, such as the seaweeds and mosses. Neverthe- 

 less most important results have been obtained from 

 the careful study of fossil plant remains. 



Comparative Morphology as a Guide to Relation- 

 ships. On the assumption that all plants are more 

 or less closely related, a comparison of the structures 

 of the living forms affords a clue to the degree of 

 relationship, and hence the great stress which is 

 laid upon the importance of Comparative Morphol- 

 ogy. In view, however, of the ready response of 

 plant structures to changes in environment, great 

 caution must be exercised in distinguishing true 

 homologies from similarities in structure due to re- 

 sponse to similar conditions. We have already 

 pointed out, for instance, that leaf-like organs have 

 developed in plants of widely separate origin, e.g., 

 seaweeds, mosses, and the higher land plants. These 



47 



