OF THE FOSSIL PLANTS OF THE COAL-MEASURES. 
379 
provisional generic name of Amyelon *. My genus Dictyoxylon, therefore, is limited, for 
the present, to the two other species already mentioned, at least so far as this country 
is concerned. M. Renault recently brought before the Academy of Sciences at Paris 
a notice of some French examples of the genus from the Coal-measures of Autun ; but 
as his memoir has not yet been published, I do not know what forms have been 
discovered by this excellent observer f . I may further observe I have recently found 
that other genera, e. g. Asterojyliyllites , sometimes possess reticulated vessels like those 
of Dictyoxylon and Amyelon. 
Dictyoxylon Oldhamium proves to be one of the most common of the plants found in 
the calcareous nodules discovered in the lower Coal-measures near Oldham and other parts 
of Lancashire and Yorkshire having the same geological horizon. The vast majority of 
the specimens are young stems or branches, rarely exceeding an inch in their greatest 
diameter : nevertheless, as I shall show in the course of this memoir, the plant attained 
to an arborescent form. It was not an articulated plant, neither was it, in the usual 
sense of the word, a dichotomous one. It had terminal branches of small size compared 
with the dimensions of the main axis, but no traces of actual leaves have been discovered 
in connexion with any specimen that I have seen. The axis possesses the three 
distinctly marked divisions of pith, wood, and bark, each of which organs requires a 
detailed description. 
The Pith. — As in the Lepidodendroid plants described in my last memoir^, this 
structure was of very small size in young twigs, and gradually enlarged with the increasing- 
dimensions of the stem, at least up to a certain stage of growth. Its average size, 
relatively to that of the entire stem, is seen in Plate XXII. fig. 1, which represents a trans- 
verse section made by Mr. Butterwortii. Fig. 2 represents the medullary axis and inner- 
most portion of the ligneous zone of a still younger stem ; whilst fig. 4 represents a 
similar section of an entire ligneous cylinder, with its contained medullary axis and a 
little of the innermost bark. Fig. 3 is a segment of the ligneous zone and the adjacent 
part of the medullary axis of another transverse section ; and fig. 5 exhibits a group of 
the cells of the true medulla, also intersected transversely. 
The pith ( a ) is an undivided parenchymatous tissue of a very regular kind. The 
intervening spaces, described by Mr. Binney as separating the cells vertically, and 
converting the pith into a discoid one, have no existence in well-preserved specimens, 
but have been the result of desiccation or some other accidental cause. The individual 
cells vary in size, but they usually range between ‘0025 and -0Q33§ : in the vertical 
section, and in perfect specimens, they often exhibit a very decided disposition to 
* See ‘Proceedings of the Royal Society,’ vol. sx. p. 436 (1872). This plant proves to he the root of 
AsteropTiyllites (Proceedings, vol. sxi. p. 397, 1873). 
t M. Renault has kindly supplied me with sections of the plant to which M. Bron&niabt had applied my 
generic name. It proves to be a Sigillarian plant. — Sept. 7, 1S73. 
X Philosophical Transactions, 1872, part ii. p. 283. 
§ As in the previous memoirs, all these measurements are given in decimal parts of an inch. 
3 e 2 
