PLAXTS OF THE COAL. 



363 



The next three orders we will discuss more fully for two reasons : 

 First, the Conifers were probably mostly highland plants, and only 

 found their way into the coal-swamps by accident, being in fact brought 

 down by freshets. The Ferns formed the thick underbrush of the coal- 

 swamps. Neither of these contributed a very large share to the mate- 

 rial of the coal-seams. The great trees of the coal-swamps, and which 

 formed the larger part of the material preserved as coal, were Lepido- 

 dendrids, Sigillarids, and Catamites. 



Again, the Conifers and Ferns were unmistakably Conifers and 

 Ferns, though certainly with characters connecting with other orders 

 and classes ; but the three orders now about to be discussed combine so 



Fig. 473 



Fig. 474. 



Fig. 472. 



Figs. 472-476.— Coal-Ferns : 472. Callipteris Sullivanti (after Lesquereux). 473. Pecopteris Strongii 

 (after Lesquereux). 474. Alethopteris Massilonis (after Lesquereux). 475. Same enlarged to 

 476. Xeuropteris flexuosa (after Brongniart). 



show dichotornous venation. 



completely the characters of widely-separated classes that there is still 

 some doubt as to their real place. For that very reason, however, they 

 are peculiarly interesting to the evolutionist. 



