722 SHORT CONTRIBUTIONS TO VARIOUS WORKS,
by the joining of two or more of them together. The form of the space necessarily left, or interstices between the sec- tions where these are distinct, varies a little ; in some cases being of nearly equal breadth throughout, and in others becoming narrower outwards, and appearing to terminate or contract about the middle of the vascular tissue, beyond which they again frequently widen outwards : these spaces often contain portions of oblique and smaller vascular cords, apparently arising at different depths in the vascular cylinder; the origin and connection of which with the cylinder is shown in the oblique section, where a single series of vessels is seen passing from it, surrounded by tissue of smaller diameter. PI. xxxviii, fig. 3 a. 3 '
"In no specimen yet examined has the course of the oblique cords been absolutely ascertained, but there can scarcely be any doubt, as suggested by Mr. Brown (to whom we are also indebted for the above observations), that those vessels after arising from the cylinder passed to the tubercles of the surface, through the thick cellular tissue which once probably occupied the larger space in the original plant. The discovery of these smaller oblique vessels is an interesting feature in the anatomy of Stiff- maria ; and they have also been pointed out by Mr. Brown as existing in Anabathra, and one of these is actually figured by Mr. Witham, in his work, (' On the Internal Structure of Fossil Vegetables,' 2nd edit., t. 8, f. 12), but considered by him (p. 41) as a section of a medullary ray. The analogous vessels existing in Lepidodendron Harcourtii, as figured by Mr. Witham (< Trans, of the Nat. Hist. Soc. of Newcastle, 1832'), appear to arise from the outer part of the vascular cylinder. A somewhat similar arrangement is also found in that division of Lycojiodiacece, consisting of Psilotum and Tmesipteris : in those genera the vascular cylinder, from which the oblique cords proceed, includes a central pith ( Brongniart, ' Hist, des Veget. Foss.,' torn, ii, pp. 44, 45).
" Fig. 3 h. Shows that the vessels are much smaller at the internal rounded portions of the wedges.
"Fig. 3 c. Exhibits the oblique cords, consisting of
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