PTERIDOPHYTA 5 1 



ORDER f, LYCOPODIALES 



Living club-mosses are largely creeping, many-branched 

 plants. Tiny moss-like leaves thickly clothe the stem while 

 the spore-bearing leaves are arranged in club-like cones. 



They embrace but four living genera, of which the two more 

 common are Lycopodium, — the common ground pine, and 

 Se!aginella. These are, however, the remnant of a very impor- 

 tant group of the Paleozoic which attained their greatest size 

 and abundance in the Carboniferous, where they included many 

 of the largest forest trees. They have since gradually declined 

 pari passu with the increasing importance of the more special- 

 ized seed plants. Lycopodiales are known from the Devonian 

 to the present. 



Among their fossil representatives are : — 



Lepidodendron (Figs. 15, 150). — This was a lofty tree of the 

 later Paleozoic, appearing in the Lower Devonian and dying 

 out in the Permian ; it was especially abundant throughout the 

 world during the Carboniferous. 



The trunks were straight and somewhat palm-like, attaining 

 at times a height of one hundred feet, and bore toward the top 

 a crown of branches. Both branches and stems always forked 

 dichotomously. The stems were densely clothed in long, simple, 

 pointed leaves, much like those of the pine, which sometimes 

 reached a length of six or seven inches. When these leaves 

 were shed, their bases remained attached to the stem, thus cover- 

 ing the bark of the branches and even of the larger trunks with 

 a distinctive spirally arranged ornamentation. Each of these 

 marks of the former attachment of the leaves is rhombic in out- 

 line and somewhat convex. It is called a " leaf-cushion." 

 The apex of its convexity represents the scar left by the fall 

 of the leaf, while the remainder of the rhombic area is formed by 

 the decurrent base of the leaf which has remained on the stem. 

 The various marks upon the leaf-cushion are the prints of 

 various parts of the stem of the leaf. Thus the central of the 



