n8 Plant Life and Evolution 



Persistence of Ancient Types. As is so fre- 

 quently the case, the most specialized of these an- 

 cient types have disappeared before their still more 

 perfect descendants, while the lower and less spe- 

 cialized forms have persisted or have left de- 

 scendants which have been able to occupy a place 

 to which more highly specialized types are not so 

 well adapted. Thus the tree-like pteridophytes of 

 the Paleozoic have given way to the more perfect 

 modern types of trees, the tree-ferns alone at the 

 present day reminding us of their past glories. But 

 the smaller ferns and club-mosses have been able to 

 compete very successfully with the humbler flower- 

 ing plants covering the floor of the forest, or drap- 

 ing the banks and hillsides in the moister parts of 

 the world. 



The fossil record bearing on the history of the 

 ferns and their allies is remarkably complete, and 

 we know from a study of the fossil forms that all 

 of the most important of the living types, i.e., ferns, 

 horsetails, and club-mosses, were clearly differen- 

 tiated during the Devonian, and possibly even ear- 

 lier. Some of the early fossil types have persisted 

 with comparatively little change down to the present 

 time, while in others the changes have become very 

 marked and the earlier types have been largely dis- 

 placed by their modified descendants, some of which 

 have adapted themselves very satisfactorily to exist- 

 ing conditions even in the temperate regions. Some 

 species, like the field horsetail and the bracken fern, 



