262 



COKDAITEAB 



[CH. 



by Williamson^ the secondary wood shows clearly marked irregular 

 concentric lines simulating rings of growth, but there is no evidence 

 of any regularly recurring variation in the diameter of the xylem- 

 elements. From the descriptions of Wilhamson and Osborne it 



Fig. 477. A, root of Cordaites. B, centre of the root enlarged; p, periderm; 

 s, space. (Kidston Coll. 1906.) 



is evident that the roots of Cordaites were profusely branched and, 

 as the latter author has shown, the method of branching points 

 to the formation of coralline roots like those of recent Cycads, 

 some Conifers and Dicotyledons. Osborne found that the cortex 



1 WilUamson (74) A. PI. ix. fig. 56. 



