﻿WHITE] fossil plants of group cycadofilices 3 s l 



The seeds described by Kidston differ but little in superficial char- 

 acters, by which alone they are known, from Rhdbdocarpos tuni- 

 catus. The genus Rhdbdocarpos, which embraces a large number 

 of Carboniferous species, includes generally large oval or oblong, 

 ribbed and sometimes more or less distinctly trigoniate fruits char- 

 acterized by an outer fleshy and an inner sclerotic test, and by chalaza, 

 micropyle, nucellar membrane and pollenic chamber, while in certain 

 silicified specimens, even pollen grains and archegonia have been ob- 

 served. It represents one of the simple types of gymnospermous 

 fruit. In these early Paleozoic types the fruit appears to have at- 

 tained its full size before fertilization, and the pollen grains appear 

 to have rested for some time in the chamber before the release of 

 the antherozoids. No embryo has been observed. 



Besides the fronds of Neuropteris, Alethopteris, and Odontopteris, 

 which have been correlated with Myelopteris, and the genera Callip- 

 teris and Linopteris (Dictyopteris Gutb.) referred to the Medullosse 

 by European paleobotanists, 1 it is probable, in the judgment of the 

 writer, that the related genera Callipteridium, and Lesleya together 

 with Megalopteris and its closer relatives are also to be placed within 

 the same enlarged group. 



Colpoxylon. — The stem fragments described as Colpoxylon by 

 Brongniart. 2 are interesting chiefly from the fact that they are mono- 

 stelic in one part and polystelic in another, the solitary stele of the 

 lower part of the stem being divided into several steles in passing 

 upward. The structure of the latter, as well as of the petioles, is 

 essentially like that of Medullosa to which the genus is evidently 

 closely related. 



The Lyginodendrece. — Passing from the Medullosea, whose foliage 

 is tvpified in Neuropteris, we will next consider the Lyginodendrece, 3 

 whose fronds, so far as known, are included in the great frond genus 

 Splienopteris. 



Heterangium of Williamson, 4 the most filicoid genus of the family, 



J The genus Nceggerathia, originally placed among the Cycadofilices by 

 Potonie on account of the arrangement of the " sporangia " on the ventral 

 surface of the scales in the large strobili, is regarded by most paleobotanists 

 as gymnospermous, though the nature of the reproduction is not definitely 

 determined. 



'See Renault, Fl. foss. bassin houill. et perm. d. Aitlitn et d'Epinac, pt. 2. 

 Paris, 1896, p. 299. 



s An excellent and succinct description of this family is given by Dr. D. H. 

 Scott, Studies in Fossil Botany, London, 1900, p. 307. 



4 Williamson. Phil. Trans., vol. 178B, 1887, p. 289; Williamson and Scott, 

 Phil. Trans., vol. i86b, 1896, p. 703; Renault, Fl. foss. bassin houill. et perm. 

 d'Autun et d'Epinac, pt. 2, 1896, p. 248. 



