So8 STUDIES IN FOSSIL BOTANY 



the presence of hypodermal ribs of sclerenchyma (Fig. 

 183, hy). 



The petiole widened out gradually into the broad 

 simple lamina, which was traversed by numerous 

 parallel bundles, derived from the subdivision of those 

 of the petiole, and branching dichotomously. The 

 larger bundles, which are crowded together in the 

 median region of the lamina, have the same structure 

 as those in the petiole ; the finer strands, toward the 

 edges of the leaf, are simplified, and no longer show 

 any centrifugal wood. Just the same simplification of 

 structure occurs in the smaller bundles of the leaf, 

 in recent Cycads. The lamina was of considerable 

 thickness, and was stiffened by the usual hypodermal 

 fibrous strands on both surfaces. The dense mesophyll 

 is said to show some traces of palisade-like arrangement. 

 The larger bundles of the lamina were connected by 

 transverse bridges of thick-walled elements. 



M. Grand'Eury : has recently identified the leaves 

 of Poroxylon in the form of carbonaceous impressions. 

 He finds that they are of great size, reaching a length 

 of a metre, with a breadth of "15 to "20 metre. They 

 are narrowed at the base, passing insensibly into the 

 petiole. 



In these leaves we have a highly remarkable 

 organisation, totally different from anything met with, 

 either in the Ferns themselves, or among the genera 

 associated under the Pteridospermeae and Cycadofilices. 

 The detailed structure is, in fact, that of a Cycad, but 

 the leaf of Poroxylon was a simple, not a compound 



1 " Sur les Rhabdocarpus, les graines et Involution des Cordai'tees," 

 Comptes Rendus, t. cxl. p. 995, 1905. 



