100 



DESCRIPTIVE CATALOGUE 



The most interesting feature of this fossil is the existence of 

 well-defined ray-tracheids, not only forming the terminal cells 

 of the rays, but also present in bands interspersed between the 

 parenchyma-cells of the ray. It is interesting in this connection 

 to notice the various conclusions which have been drawn by 

 different writers on the discovery of fossils from the Upper 

 Cretaceous, which show some degree of development of these 

 ray-tracheids. Jeffrey & Chrysler (1906) described t\vo 

 species of Pltyoxylon from the Upper Cretaceous of North 

 America. In these two specimens no ray-tracheids were 

 fouud ; they therefore infer that " there can be little doubt, that 



c. 



Text-fig. ^A.Tityoxylon Sewardi, sp. nov. Tangential section of medullary 

 ray, showing the ray-tracheids, tr., alternating with larger contents- 

 containing parenchyma, c. No. V. 1410 c. 



in the peculiar structure of the rays we have to do with an 

 ancestral feature. . . . The cells on the margins of the rays 

 in our Pityoxylon are, moreover, related to the central cells 

 of the rays and to each other by simple pits, and not by bordered 

 pits as is the case with the marginal tracheids. It is obvious 

 that the ray-structure of Pinus underwent a great change in 

 the passage from the Mcsozoic to the Tertiary period." The 

 conclusion, based solely on the structure of two specimens from 

 one locality of the Upper Cretaceous, is that "the appearance 

 of marginal tracheids in the rays of Pinus is comparatively 



