266 



THE ANATOMY OF WOODY PLANTS 



scalariform in their sculpture, but tend, like those of the arboreal 

 Lycopodiales, to develop the pitted condition. The pits, whether 

 scalariform or rounded, were found equally on radial and tangential 

 surfaces of the elements of the secondary wood, a condition par- 

 alleled in the ancient treelike representatives of the Lycopodiales. 

 The outer region of the figure shows the soft tissues in a condition 

 of relative disorganization, which does not make their discussion 

 profitable. 



The most interesting general features presented by the anatomy 



of the stem in 

 Sphenophyllum are 

 its essentially pro- 

 tostelic character, 

 the peculiar 

 organization of the 

 rays, and the tan- 

 gential as well as 

 radial pitting of 

 the tracheids. The 

 leaves and roots 

 are not well known 

 as to their ana- 

 tomical organization and in the actual state of our ignorance mani- 

 fest no features of unusual interest. 



The Calamitaceae are distinguished from the Sphenophyllaceae 

 anatomically by the siphonostelic organization of their central 

 cylinder. In the more ancient types of Calamites the ridges and 

 furrows of the stem were continuous at the nodes, precisely as is 

 the case in Sphenophyllum. Moreover, in the Archaeocalamitaceae 

 the leaves divided dichotomously. In more modern calamitean 

 types the alternation of the ridges and furrows in the nodal region 

 began to become a marked feature of organization except in the 

 cones or reproductive axes, which adhered to the more ancient 

 topography with non-alternation at the nodes. 



Fig. 189 illustrates the organization of a younger stem in a 

 calamite. The outer region of the axis has generally disappeared 

 as a result of fossilization, but the woody and medullary regions are 



FIG. 189. Transverse section of a small stem of 

 Calamites. 



