THE PENNSYLVANIAN PERIOD. 



597 



Andes, have but slender stems 30 or 40 feet long, whereas the Carbon- 

 iferous calamites reached a foot or two in diameter and probably 60 to 

 90 feet in height. The calamarians had hollow stems, or a core of 

 pith only, and casts of the interior are among the most common forms 

 of the fossil (Fig. 279, a). The 

 constriction at the node in the cast 

 is due to the internal thickening 

 of the walls, the complement of 

 a ring-like expansion externally. 

 The greatest divergence of the stem 

 from the modern forms consisted 

 in a secondary growth, apparently 

 a means of strengthening the 

 stem to meet the exigencies of great 

 growth. The arrangement of the 

 stem tissues was also much more 

 complex than in modern forms. 

 More notable geologically than 

 either of these features was a great 

 development of cork on the outside, 

 sometimes reaching a thickness of 

 two inches or more. This probably 

 implies adaptation to some climatic 

 or other physical condition. Cala- 

 mite stems have been found show- 

 ing wounds which had been healed 

 over by wound cork, as in modern 

 times. The branches from the main 

 trunk were comparatively few, and placed in whorls. The leaves 

 also were placed in whorls (Fig. 279, b) and were apparently very much 

 bedwarfed from some ancestral form, but not so much so as in the 

 modern type in which the leaves have almost disappeared. In the 

 Devonian Archeocalamites, the leaves were forked; in the Carbon- 

 iferous calamites, they were lanceolate, implying a progressive sim- 

 plification of the leaf. The upper and lower sides of the leaves were 

 strongly contrasted, the stomata deeply set, and the palisades radially 

 arranged; in short, the structure was of the type adapted to dry weather 

 (xerophytic) as in the pine and in many desert plants, and also, strangely 



Fig. 279. — Carboniferous Equisetales and 

 Sphenophyllaies : a, Calamites cistii; b, 

 Annularia sphenophylloides; c, Spheno- 

 phyllum longifolium. 



