POROXYLEAE 501 



known). Poroxylon is a genus in which the available 

 data chiefly relate to the vegetative structure ; such 

 evidence as we possess concerning its organs of repro- 

 duction will be considered later on. Our present, very 

 complete knowledge of the anatomical structure, which 

 is preserved in astonishing perfection, was due in the 

 first instance to the investigations of the two French 

 palaeobotanists, MM. Renault and Bertrand. 1 



The genus was originally discovered in the Permo- 

 Carboniferous deposits of Grand Croix and Autun, in 

 France ; an allied species has recently been recorded 

 from the Lower Coal-measures of Lancashire. 



The two best -known French forms, Poroxylon 

 Boyssetii (which includes the specimens first dis- 

 covered, and described by M. Renault in 1879) and 

 P. Edwardsii, only differ from each other in un- 

 important characters, which may or may not be of 

 specific value. 



The stems of these plants were comparatively slender, 

 the specimens described not much exceeding half an 

 inch in diameter ; they bore spirally arranged leaves, 

 separated from each other, for the most part, by rather 

 long internodes ; the French authors have worked out 

 the phyllotaxis, from the course of the leaf-trace bundles, 

 and found the divergence between two successive leaves 

 to be ^ 3 -. The leaves themselves were very different 

 in character from those of any of the Pteridosperms, as 

 at present known. They were broad, thick, simple 

 leaves, inserted on the stem by a definite petiole, and 

 tapering towards the opposite extremity. The lamina 



1 Renault, Tiges de la Jlore carbonifire, 1879; Bertrand et Renault, 

 " Les Poroxylons," in Archives bot. du Nord de la France, 1886. 



