BIBLIOGRAPHY. 



133 



sufficient to confirm what I have ah-eady stated in the boJy of the memoir, that we need 

 only remove the central cellular medulla of the plant in question to convert it into a trae 

 Diploxylon ; the identity of the two, so far as structural type is concerned, is as close as 

 it can be even in its minuter details. Such being my conviction, I propose to designate 

 the plant represented in figs. 8 — 11 Dijjioxi/Ion vasculare, and to apply Corda's name of 

 D. cycadoideum to figs. 21 — 23. 



"The plant represented by figs. 33, 34 distinguished by its large medullary axis and 

 by the deeply fluted aspect of the interior surface of its ligneous zone, I propose to 

 designate Biploxyhn cylindricum ; whilst a fourth form, exhibiting some different features 

 yet to be noticed, I would term D. stiymarioidemn. So far as the general structure of 

 the stem is concerned, the last-named plant does not differ from the other Diploxylons. 

 The cellular medulla has disappeared, but there remains the medullary ring of barred 

 vessels, surrounded by the exogenous ligneous zone. The primary and secondary medul- 

 lary rays also appear, but neither of them occurs so abundantly as in the other species. 

 Moreover, in the radial vertical sections, the vascular bundles occupying the primary rays 

 exhibit a different aspect from those of the other species described, and approach nearer 

 to what exists in Stiymaria ficoides. This is represented in fig. 23, h. The vascular 

 bundle {m) appears to be derived from the body of the ligneous zone, and not from its 

 medullary surface. It is composed of smaller vessels than those seen at e ; but we find 

 that at e these vessels diminish in size, and approach in magnitude those of the bundle w^; 

 not only so, but, whilst the upper extremities of the small vessels of m exhibit the perpen- 

 dicular arrangement indicating that they belong to the part of the woody zone in which 

 they occur, the lower extremities of the large vessels (<?) are deflected in the direction of 

 those of the foliar bundle, which is never the case with the corresponding ones of the 

 other forms of Diploxylons. The lower margin of the foliar bundle is cut off" in this 

 section by an oblique, sharply defined line ; this indicates that the large vessels at e have 

 been sharply deflected to the right and left of the bundle, to allow the latter to pass 

 between them. All these appearances correspond so closely with what we find in 

 Stiymaria that for a long time this plant seriously perplexed me ; but it appears to be a 

 true Diploxylon, since it has the vascular medullary cylinder of that genus as well defined 

 as in any other species. This cylinder is never found in Stiymaria ficoides. It has been 

 more especially in connection with this species of Diploxylon, though not exclusively, that 

 I have found the peculiar bark represented in figs. 54 — 57. It is possible that this plant 

 may, like Stiymaria, prove to be the uppermost part of a root of some of the other forms, 

 though I have never yet found it associated with any rootlets ; or it may be a fragment 

 from the base where stem and roots imited. 



" Amongst the numerous other interesting plants for which I am indebted to G. Grieve, 

 Esq., of Burntisland, in Fifeshire, is a well-marked Diyloxylon, closely allied to D. cyca- 

 deoidenm. Like the rest of Mr. Grieve's specimens, it is from the deposit of the Lower 

 Carboniferous age which occurs embedded amongst trappean rocks at Pettycur Bay. 



