458 PENNSYLVANIAN PERIOD 



LIFE 



With this period the chief biological interest shifts from sea to 

 land, and centers in the vegetation and the amphibians. 



Plants 



Plant life was very abundant in this period, and its record is 

 unusually full and perfect. Its completeness has doubtless given 

 this flora an undue prominence over those which preceded and suc- 

 ceeded it; yet it was really a great period in the history of plant life. 

 Angiosperms (flowering plants, p. 685), the dominant plants to-day, 

 had not yet appeared, but gymnosperms (the group to which pines 

 belong) were abundant, and pteridophytes (ferns arid related plants) 

 probably made their greatest display at this time. All the great 

 divisions of this group (p. 685) were present, and all of them were 

 nearly or quite at their climax. Of lower plants, little is known. 

 The most rapid evolution of floras was perhaps in the Pottsville 

 epoch. Half the genera of that epoch scarcely survived it, and few 

 of them lived after the Allegheny epoch. 



The early floras were widely distributed. Thus three floras in 

 Asia Minor may be correlated severally with three floras of the 

 Pottsville series. The place of origin of these early floras is not 

 known with certainty, but present evidence points to western 

 Europe and eastern North America, with an Arctic land connec- 

 tion. The late Pennsylvania floras are less sharply separated from 

 the early ones in North America than in Europe. The later floras 

 indicate greater diversity of climate than the earlier. 



The dominant plants of the period belonged to five groups: 

 (i) the horse-tail family (Equiseta), (2) sphenophylls, now extinct, 

 (3) lycopods, or club mosses, (4) fern-like plants (pteridos perms), 

 and (5) Cordaites, a group of gymnosperms. To this list ferns 

 should perhaps be added. 



Ferns were a minor element of the Pennsylvanian flora, though 

 fern-like leaves are the most abundant of the plant fossils. It is 

 now known that most of them belonged to seed-bearing plants and 

 not to ferns. Nevertheless, true ferns were present. Species still 

 live which, so far as outward form is concerned, might be referred 

 to Carboniferous genera. 



The horse-tail group (Equisetales) was represented by calamites 

 (tree horse-tails), a conspicuous element in the Pennsylvanian flora. 

 They must have been graceful trees, of the same general habit as 



