LIFK 



461 



records a continuous decline from the Pennsylvanian period, when 

 it was at its best. 



Recent studies have shown that the graceful, slender plants with 

 whorled leaves, referred to the genus Sphenophyllum (c, Fig. .397), 

 formerly classed as calam- 

 ites, should be made a class 

 (Sphenophyllales, p. 685) by 

 themselves. Their interest 

 lies chiefly in the fact that 

 while they have certain cal- 

 umuriun features, they have 

 others possessed by lyco- 

 pods. This is interpreted 

 to mean that these two 

 groups (calamarians and ly- 

 copods) were united with 

 Sphenophyllales in a com- 

 mon ancestral form. 1 The 

 stems were long, slender, and 

 apparently weak, and a 

 climbing habit has been in- 



Iferred. The leaf structure 

 suggests a shady habitat, 

 perhaps one of undergrowth. 

 The class, represented in 

 the Devonian, had its climax 

 in the middle Pennsylvan- 

 ian, and continued into the 

 Permian and possibly later. 

 In size Lycopods (p. 685) 

 were the master group of 



the Coal flora. They were represented by trees of large size 

 which had the highest organization reached by the pteridophytes. 

 From this high estate, they have since fallen to prostrate 

 or weakly ascending plants of moss-like aspect (club mosses 

 and ground pines.) The chief genera were Lepidodendron and 

 Si^illaria (Fig. 395), of which the former was the earlier and sim- 

 pler type. Both take their names from the leaf-scars (lepidos = 

 I scale, sigilla = seal) which the trunks retained (Figs. 398 and 399). 

 1 Seward, Fossil Plants, p. 413; Scott, Studies in Fossil Botany, p. 494. 



I 



Fig- 397- CARBONIFEROUS EQUISETALES 

 AND SPHENOPHYLLALES: a, Catamites cistii; 

 b, Annular ia splienophylloides; c, Spheno- 

 phyllum longlfolium. 



