﻿378 SMITHSONIAN MISCELLANEOUS COLLECTIONS LVOL. 47 



known only by the anatomical structure of their stems and petioles; 

 that fronds have been definitely correlated with but four generic 

 types; and that fruits are known in but three. Concerning the 

 microsporangiate organs, we have hardly more information than we 

 have respecting the Cycadofilic fruits. 



The group appears to have been confined to the upper Paleozoic, 

 and almost exclusively to the Carboniferous, including, in a broad 

 sense, the Permian. The widely diversified associated or contem- 

 poraneous ferns are overwhelmingly eusporangiate, most of them 

 showing closer affinities with the Marattiacese than with any other 

 living family, though imperfect rings of various forms several cells 

 in width, or may be in thickness, characterize some of the rarer fern 

 genera. The pteridophytic comparisons are therefore with the 

 Marattiacese, the Ophioglossacese and, to a less extent, with the 

 Osmundacese and the Lygodiacese. The gymnospermic characters 

 are principally Cycadean, though Cordaitean, and, in a minor de- 

 gree, Araucarian characters appear less prominently in a few of the 

 genera. 



Types Generally Regarded as Cycadofilic 



Clado.xylon. — One of the oldest though less known types with 

 which we have to do is Cladoxylon of Unger, from the Lower 

 Carboniferous of Thuringia. 1 The reference of this genus to the 

 Cycadofilices rests on the characters of the stems which are poly- 

 stelic. The steles, or vascular axes, as seen in transverse section 

 are dilated radially, each stele including a broad central band of 

 primary wood with one or several groups of spiral tracheae, or primi- 

 tive xylem elements, at the border. In the earlier stages the stem, 

 even when of considerable size, is typically filicoid ; but in most of 

 the older stems each stele develops a zone of secondary wood with 

 more or less numerous medullary rays. The tracheides of both 

 primary and secondary wood are scalariform. The petioles show a 

 structure distinctly characteristic of ferns, and, but for the secondary 

 wood, the pteridophytic nature of the stems would be unquestioned. 



The Medullosece. — Among the Paleozoic stems longest and best 

 known by their internal structure are those of Cotta's genus Medul- 

 losa. These stems, 2 sometimes a foot or more in diameter, are 

 polystelic (see plate i.iv), the steles being irregular in form and dis- 



'See Solms-Laubach, Abh. d. k. Pr. geol, Landcsanst., Heft, 23, 1896, p. 51. 



2 See Weber and Sterzel, Beitragc sur Kcnntniss der Medullosece; Ber. 

 naturw. Gesell. zu Chemnitz, vol. xiu, 1896, p. 44. See also Solms-Laubach, 

 Bot. Zcit., 1897, p. 175; Scott, Phil. Trans., vol. 191, B, 1899, p. 81; Goeppert 

 and Stenzel, Palaontographica, vol. xxviii, 1881, p. 12.3. 



