3 o6 



THE ANATOMY OF WOODY PLANTS 



are conspicuous by their absence. Although some indication of 

 the existence of annual diversities of temperature is supplied 

 by certain cordaitean stems, the organization of the annual ring 

 in such cases is extremely simple, and even the differentiation 

 involved in the presence of terminal tangential pitting is not seen, 

 as may be ascertained by reference to Fig. 219, representing a 

 specimen from Lancashire, England, in stereoscopic view under 

 a high magnification. It is apparent from the figures that the 



US 



FIG. 216. Part of a transverse section of a cordaitean stem (after Scott) 



secondary xylem of Cordaitales was of very simple structure and 

 that the rays, unlike those of the two tribes considered in a 

 previous chapter, were usually a single row of cells in width. 

 This narrowness of the strands of radial parenchyma is shared 

 by the Cordaitales with the Ginkgoales and the conifers. The 

 wood, like that of other Paleozoic gymnosperms, was entirely 

 without longitudinal parenchymatous elements, and the bor- 

 dered pits were strictly confined to the radial walls of the 

 tracheids. 



Another interesting feature of the organization of the xylem 

 in cordaitean forms was the extremely long region of transition 

 between the spiral elements of the protoxylem and the first pitted 



