354 PROFESSOR W. C. WILLIAMSON ON THE PLANTS 



enlargement. It is a moot point whether or not its dia- 

 meter is at all affected by the subsequent growth of the 

 tree; but, if it is so affected, the change tends to a diminu- 

 tion of diameter, rather than to an enlargement. But, 

 be this as it may, it is certain that Sternbergia has been 

 characterised by a remarkably large medullary cavity, and 

 that a similar feature is exhibited by the examples of Mr. 

 Witham's genus Pinites; neither is there any material 

 difference in the structure and arrangement of their pleur- 

 enchyma, though they present slight diversities in the form 

 of their medullary rays. These points of affinity render it 

 probable, either that they have contained a structure like 

 Sternbergia, which has been overlooked, or that the whole 

 of the cellular tissue has disappeared prior to fossilization. 



In the Lancashire coal-field, as elsewhere, fragments of 

 coniferous wood are not unfrequent. Mr. Dawson consi- 

 ders that the fragments of mineral charcoal, which are of 

 common occurrence, may be of the same nature. Such, 

 however, is not the case. The structure of the fibres or 

 ducts (whichever they may be), in the latter substance, are 

 peculiar and distinct, as has been already pointed out by 

 Dr. J. Hooker. The latter observer looks upon the structure 

 as allied to the tissues of Cycadeae. They appear to me to 

 exhibit a more marked resemblance to the perforated ducts 

 of Tmesipteris. — {See Brongniarfs Veg^taux Foasiles, Vol. ii. 

 Tab. 11, fig. G h). Be this as it may, it is certain that they 

 are very different from coniferous pleurenchyma. The latter 

 tissue, however, is sufficiently abundant. I possess one 

 remarkably fine specimen of fossil wood from near Wigan, 

 in which a thick branch passes quite through the wood, like 

 a knot in a piece of common deal. In the centre of the 

 branch there is a pith of considerable size, though nothing 

 approaching to the dimensions of that of fig. 10. I believe 

 it to be very probable that this specimen belongs to the same 

 genus of coniferae as the Sternbergia, if not even to the same 



