722 SHORT CONTKIBTJTIONS 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. PL xxxviii, fig. 3 a." 



"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 Stig- 

 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 Lycopodiacece, 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.,' tom. ii, 

 pp. 44, 45). 



" Fig. 3 b. Shows that the vessels are much smaller at 

 the internal rounded portions of the wedges. 



"Fig. 3 c. Exhibits the obhque cords, consisting of 



