146 



POSSIL PLANTS. 



names are only provisional, but I think it better that they should remain until we know 

 more of the fructification of the plant. 



In all the large specimens of Sigillaria vascularis hitherto observed the zone of lax 

 parenchyma intervening betwixt the inner and outer radiating cylinders is so disturbed 

 that we have been unable to absolutely prove that the vascular bundles which traverse the 

 one are connected with those that traverse the other, however probable it may appear 

 that such is the case. In the small specimen, where this part of the plant is seen 

 in contact with the inner radiating cylinder, and extending to the leaf-scars, it proceeds in 

 a nearly horizontal direction, as previously shown in the woodcut (fig. 5), very differently 

 to the vascular bundle of the Lepidodendron Harcourtii (No. 31) described in this 

 Monograph, which at first proceeds from the medullary sheath in a nearly vertical 

 direction, and then makes a gradual curve to the leaf-scar. It appears to me nearly 

 certain, as some authors have suggested, that the large vascular bundles which traverse 

 the inner radiating cylinder, and proceed through the outer one to the leaves, are really 

 foliar bundles, and not medullary rays, and that we must hmit the term " medullary ray" 

 to the single- and double-celled rays found in the tangential sections of the inner 

 radiating cylinder. 



In examining the structure of Coal-measure Plants we labour under great difficulties, 

 owing to the fragmentary state of the specimens, and we have to collect evidence gradually 

 and with patience. It has never been my practice to pretend to do much more than to 

 collect the best specimens, and to carefully describe them, in accordance with the advice 

 of that great botanist, the late Dr. Robert Brown, who more than once stated to me 

 that such was the course he should recommend, and which he himself would adopt. To 

 other more experienced botanists is left the task of comparing the ancient with the 

 modern flora. 



To those who asserted confidently that Slgillaria vascularis had a medulla of 

 parenchyma, and not of barred tubes, specimen No. 39, hereinbefore described, is 

 adduced as evidence in favour of my views and against theirs ; and to those who con- 

 tended that Stigmaria had a medulla of parenchyma, and not of barred tubes as alleged 

 by me, the specimen No. 44 is brought forward in support of my view that such root 

 had a medulla of barred tubes and cells. Both these specimens, to my mind, appear to 

 prove that Slgillaria vascularis had for its root a Btigmaria with a medulla of barred 

 tubes and cells similar to those found in its own stem, whatever kind of Stigmaria other 

 Sigillario: had for their roots. But up to this time, with the exception of No. 46, to 

 my knowledge, no specimen has been described and figured in such a perfect state of 

 preservation, as to prove satisfactorily the true nature of the pith of the root. This remains 

 to be done. 



Por all the numerous species of Sigillaria — and their number is very great — little 

 evidence has been obtained to prove the nature of their respective roots, either by 

 similarity of structure or absolute connection. 



