1899] ON THE ANATOMY OF FOSSIL PLANTS 369 



also by their endogenous origin ; tangential sections through the cortex 

 of the parent plant, and passing also through an adventitious root, 

 showing the latter as a complete organ possessing a cortex and 

 epidermis of its own, whereas a similar section through the base of a 

 branch would show only the vascular tissues passing outwards from the 

 stele of the main stem. The authors point out that — " The typical 

 roots of Lyginodendron, before the commencement of secondary growth, 

 often bear a striking resemblance to the smaller roots of recent 

 Marattiaceae." l 



The roots exhibit secondary thickening in a quite normal manner, 

 but curiously enough become more like certain dicotyledonous roots 

 (e.g. Cucurbita Pepo) than those of cycads or ferns. The peculiar and 

 characteristic appearance presented by the older roots, in which the 

 secondary xylem shows a peculiar disposition, generally into five or six 

 large wedges, separated from one another by wide parenchymatous 

 wedges, is simply due, as also in the Cucurbita mentioned above and 

 figured by De Bary, 2 to the fact that, whereas opposite the primary 

 phloem groups great masses of xylem separated by narrow medullary 

 rays are formed, thus building up the wedges of wood, opposite the 

 primary xylem the cambium forms mainly parenchyma. 



All the specimens of Lyginodendron, of which the structure is 

 described by Williamson and Scott, are comparatively small in size 

 (not exceeding about 4 cms. in diameter), while many of the 

 cortical impressions, if they really belong to Lyginodendron, represent 

 plants which must have attained the dimension of trees. Mr. 

 A. C. Seward has described, under the name of L. robmtumf the 

 structure of a much larger specimen, of which the diameter of the 

 woody cylinder and pith alone attains 14 cms. The preservation of 

 this specimen is not as good as in L. Oldhamium (the ordinary form), 

 but traces of the primary bundles can be seen, as also an internal ring 

 of centripetal xylem, similar to what has been described in L. Old- 

 hamium as anomalous wood. The author poiuts out that there is 

 great similarity between L. robustum and a type from Autun, described 

 in 1879 by Eenault as Cycadoxylon Fremyi, and adds that " the term 

 Cycadoxylon proposed by Eenault, if extended in its application, might 

 serve as a general generic designation for plants possessing secondary 

 xylem closely resembling that of recent Cycads." 4 



In the species of Permo-carboniferous Poroxylon described by MM. 

 Bertrand and Eenault, 5 we find a similar arrangement of parts to that 

 in Lyginodendron. They too must have formed small trees. As in 



1 "Further Observations," etc. Tart. III. p. 738. 



2 "Comparative Anatomy of the Phanerogams and Ferns," English Edition, p. 474, 

 fig. 204. 



3 "A Contribution to our knowledge of Lyginodendron," Annals of Botany, March 

 1897. 



4 Loc. cit., p. 84. 



5 ''Recherches sur les Poroxylons," Arch. lot. da Nord dc la France, 18S6. 



