ORGANIZATION OF THE FOSSIL PLANTS OF THE COAL-MEASURES. 705 
IL—LYGINODENDRON. 
The history of this genus has been given in a previous memoir.* The fossil in 
question was first described by Brnnzy, in 1866, under the name of Dadoxylon 
Oldhamium, was next transferred by WiLL1AMson, in 1871, to his genus Dictyoxylon. 
and was subsequently placed by him in Gourtir’s genus Lyginodendron, previously 
known from cortical impressions only. Lyginodendron is now characterized by its 
structural features, which are quite distinct from those of any other genus. Its 
relation to the cortical impressions is a question of some difficulty, to which we shall 
return below (p. 741). 
All the forms with which we are concerned may be provisionally referred to the 
same species, or rather type, namely, Lyginodendron Oldhamium. Its stems are 
among the commonest fossils preserved in the calcareous nodules of the coal-measures 
of Lancashire and Yorkshire, and they have also been found in those of Langendreer 
and Orlau, in Germany, but not, it seems, in any of the French coal-fields. The 
Sphenopteroid foliage of the plant is often found in association, and sometimes in 
connection, with the stem. The petiole is identical with the fossil formerly described 
as Rachiopteris aspera, as was shown in Memoir XVII, above cited. We have 
already recorded our discoveryt that Kaloxylon Hookeri represents the adventitious 
roots of Lyginodendron. The evidence for these conclusions will be given in later 
paragraphs (see pp. 725 and 733). 
The abundance of the material and its remarkably perfect preservation have placed 
us in a very favourable position for working out the structure, and have enabled us 
to distinguish characters which are constant and essential from mere individual 
peculiarities. Variations of the latter kind are rather frequent and include some 
interesting anomalies, 
A.—TuHE Stem. 
1. General Structure. 
The stems, which we are about to describe, are of very variable dimensions. The 
smallest specimens do not exceed 3 millims. in diameter ; the largest undoubted stem 
of Lyginodendron which we possess attained a diameter of about 4 centims. We 
leave out of consideration for the present both Mr. NeILp’s specimen} and the cortical 
* Witiiamson, “Organization of the Fossil Plants of the Coal Measures,” Part IV., ‘ Phil. 
Trans.,’ 1873, p. 377. 
The other memoirs of the series relating to Lyginodendron are: Part VI., 1874, vol. 164, Part IL, 
p. 675 (Rachiopteris aspera, now known to be the petiole of Lyginodendron) ; Part VII., 1876, vol. 166, 
Part I., p. 1 (Kalorylon Hooker’, now known to be the root of Lyginodendron); Part XIII., 1887, 
vol. 178, B., p. 289 (Kalowylon) ; Part XVIL., 1890, vol. 181, B., p. 89. 
See also Soums-Lavsaca, “ Fossil Botany,” English translation, 1891, p. 358. 
+ WILLIAMSON and Scort, “The root of Lyginodendron Oldhamium,” ‘Roy. Soc. Proc.,’ vol. 56, 1894. 
t See “ Organization,” Part IV., p. 386. 
MDCCCXCV.—B. 4 ¥ 
