BIBLIOGRAPHY. 



125 



purpose of examining the inner radiating cylinder, and in every case medullary rays or 

 bundles were found traversing it, just as you find in the same part of Stigmaria. On 

 the outside of the inner cylinder, at the extreme part of the zone of coarse and lax cellular 

 tissue which bounds it, are some circular openings from which spring the wedge-shaped 

 masses of quadrangular, tubular, or elongated utricles which form the outer radiating 

 cylinder. The lax cellular tissue has nearly always been displaced and disarranged in 

 the process of mineralization, and sometimes the outer radiating cylinder, and the cir- 

 cular orifices connected with it, have been pushed towards the inner cylinder. This may 

 be the case in Brongniart's specimen, and have caused him to suppose that the medullary 

 rays or bundles originated only on the outside, and were not joined to those which 

 traversed the inner cylinder. So far as my larger specimens show there were medullary 

 rays, Avhich had their origin next the central axis, passed through the inner cylinder, and, 

 after traversing the zone of lax cellular tissue outside the latter, apparently communicated 

 with similar rays or bundles of vessels of much larger size, which are always found 

 traversing the outer radiating cylinder, and then went on to the leaves on the outside of 

 the stem. ...... 



" In the specimens Nos. 2 and 3 the outer radiating cylinders are nearly an inch and 

 a half in breadth, of thick-walled tubes or elongated utricles arranged in radiating series 

 and diverging from a circular opening ; while in Brongniart's Sipllaria elegans the outer 

 radiating cylinder was not more than iVth of that breadth. Probably my specimens 

 may not prove to be of the same species as that of the celebrated Autun specimen ; still 

 they may be of the same genus, although of considerably greater age. But they have 

 the greatest resemblance to the Sigillaria vascularis described by nie in a paper read 

 before the Geological Society and printed in its ' Journal ' (vol. xv, p. C36). All the 

 specimens described in that communication, as well as those in the present, were obtained 

 by me from the same seam of coal, but at different places ; still the two, namely the 

 large-ribbed-and-furrowed specimens and the small rhomboidal-scarred stems, are always 

 found associated together, and they can be traced gradually passing from one into the 

 other. These facts, when taken in connection with the similarity in structure in the 

 central axis, the internal radiating cylinder, the space filled with lax cellular tissue 

 between the latter and the outer radiating cylinder diverging from circular openings, 

 clearly prove that the smaller specimen is but the young branch of the older stem ' No. 2.' 

 It is true that the earlier authors who have written on these plants would scarcely have 

 admitted a ribbed and furrowed Sigillaria to have been so intimately connected with a 

 rhomboidal-scarred plant, but it is now generally allowed that such difierences in external 

 characters would afibrd no grounds for ignoring the structural similarity of the 

 specimens. Undoubtedly the small Sigillaria vascularis was part of a branching stem, 

 for in my cabinet there is a specimen clearly showing two internal radiating cylinders 

 just at the point where the branches dichotomized, as shown in the woodcut (fig. 2), so 



often met with in Lepidodenclron} 



1 See Plate XIV, fig. 4, of tliis Monograph. 



