£40 J. W. DAWSON ON A SPECIMEN OF DIPLOXYLON 



ligneous lining, have been of considerable firmness, which would, in- 

 deed, seem to be implied in the manner of its preservation within the 

 hollow bark. 



Xo trace remains of the thick inner bark, which is represented by 

 sandstone ; and, as usual in these trees, the outer bark consists of 

 structureless coal. The outer surface of the sandstone cast shows lon- 

 gitudinal striation ; but the ribs, if present, are very indistinct ; and 

 only a few somewhat remote and indistinct depressions remain as 

 indications of the leaf-scars. The roots, as stated by Mr. Hill, show 

 a delicate transverse wrinkling, which may be an effect of pressure. 

 In one small portion only could I recognize on them the remains of 

 the stigmarioid areoles. 



When treated with an acid, the calcareous matter is removed and 

 the wood remains as a crumbling dark brown mass, which shows the 

 structure very perfectly when diffused in water or Canada balsam. 

 When this brown substance is ignited it burns with scarcely any 

 flame, and leaves a reddish ash, in which the bars of the scalariform 

 tissue are still quite apparent. 



In some parts of the axis the medullary cylinder becomes reduced 

 in size, and the inner scalariform cylinder proportionally thickened. 

 Towards the top of the axis there is an indication of bifurcation,which 

 may, however, be a deceptive appearance resulting from mechanical 

 splitting due to decay. 



The structures above described are obviously those of Diploccylon 

 of Corda ; and the tree may be regarded as a Sigillaria of this type, 

 the only well-characterized one yet found in the Nova-Scotia coal- 

 field. In comparison with the axes of Sigillarice which I have de- 

 scribed in former papers presented to this Society, it agrees in the 

 general arrangement of the tissues, but differs considerably in their 

 character. The pith cylinder is smaller and not Sternbcrgian. The 

 scalariform tissue of the inner woody cylinder and medullary sheath 

 is much coarser. The outer cylinder, instead of pseudo-scalariform 

 and porous tissue, like that of Cycads, has coarse scalariform tissue. 

 In these respects the trunk resembles those recently described by 

 Williamson*, and is also like specimens from Arran shown to me 

 some years ago by Mr. Carruthers. From the examples given by 

 the former, I cannot doubt that such trees come within the limits of 

 the genus Sigillaria, as determined by the markings of the bark ; 

 and that they belong to that low typo of these trees in which the 

 woody matter, while arranged in an exogenous manner, is wholly 

 scalariform, and with the medullary rays little developed. As Wil- 

 liamson has shown, these trees approach closely to Lepidodendra in 

 their structure. On the other hand, the Sigillarice of the type of 

 S. elegans of Brongniart, and of S. sjnnulosa of Renault and Grand'- 

 Eury, have a somewhat higher organization, and point to the still 

 more elevated type described by me in 1870. There would thus 

 appear, as I pointed out in my paper on the structures of coal in 

 1859, and in that on the conditions of accumulation of coal in 18G5, 



* Transactions of the Royal Society. 



