S3o STUDIES IN FOSSIL BOTANY 



The character, from its frequency in Cycadofilices and 

 the early Gymnosperms, appears to have considerable 

 taxonomic significance — a suggestion borne out by 

 recent work on the occurrence of the double leaf-trace 

 in recent Gymnosperms, and in Angiospermous seed- 

 lings. 1 



The large stems of Cordaiteae are known to have 

 formed a thick and complicated bark, but its develop- 

 ment has not yet been satisfactorily worked out. 



3. The Root. — Mixed with the remains of leaves 

 and branches of Cordaites, silicified specimens of roots 

 have also been found ; they agree so well in histological 

 structure with the stem, that there is no reason to 

 doubt the correctness of M. Renault's conclusion, that 

 they belonged to the same plants, though I am not 

 aware that roots showing structure have yet been 

 found in actual connection with the stem. In the 

 French specimens the roots are diarch, with a broad 

 zone of secondary wood. The elements of the proto- 

 xylem are spiral, the rest of the primary tracheides 

 scalariform, while the surrounding secondary zone is 

 made up of pitted tracheides and medullary rays, and 

 agrees in all essential respects with the wood of the 

 stem. The root is limited on the outside by a broad 

 zone of periderm, which, from M. Renault's description, 

 would appear to have been derived from the external 

 cortex. This is unusual in Gymnospermous roots, and 

 the point seems to deserve further investigation. 



Our Fig. 191 is taken from a root known as Amyelon 



1 Miss E. N. Thomas, " A Theory of the Double Leaf-trace, founded 

 on Seedling-Structure," New Phytologist, vol. vi. 1907, p. 77. 



