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III. — On a new variety of Vascular Tissue, found in a fossil wood 

 from the London Clay. By James Scott Bowerbank, Esq., F.G.S. 



Read October 21, 1840. 

 The singular variety of vascular tissue which is the subject of this 

 paper, occurs in a fossil dicotyledonous wood from the London clay of 

 Heme Bay, in Kent. The texture of the mass is unlike the greater 

 part of the fossil woods of this formation, which are either composed 

 of solid carbonate of lime, as in the specimens from Harwich and its 

 neighbourhood, or of iron pyrites, as in the small pyritical fragments 

 of stems and branches so numerous among the shingle beneath the 

 clay cliffs of the north shore of Sheppey. The specimen under consi- 

 deration is very similar in appearance to Bovey coal, but more friable 

 and carbonaceous. With a low power a longitudinal section of the 

 wood has very much the same appearance as a similar section of beech 

 wood. When a thin slice is viewed as a transparent object with a 

 power of 100 linear, it exhibits numerous large vessels, the greater 

 part of which are of that variety of anmdar vessel which has the annu- 

 lations very much interrupted and divided into numerous portions of 

 various sizes. Occasionally large vessels are seen, thickly covered 

 with minute dots, having a dark line passing over the centre of each, 

 at right angles to the axis of the vessel, (PI. ii. fig. 1). If we increase 

 the power to 800 or 1000 linear, the structure of this curious appen- 

 dage to the discoid organs or dots is rendered apparent, and we find 

 that each of these transverse markings is composed of two lines, sepa- 

 rated from each other at their centres but uniting at either extremity, 

 (PI. ii. fig. 2). In most cases these lines do not extend over the sur- 

 face of more than one dot, and their united ends project slightly be- 

 yond its margin, but a few instances may be seeu of their extending 

 over two, three, and even four dots, and then the lines are observed to 

 expand to the greatest degree over the centre of each of the dots, and 

 to approach each other slightly in the spaces between them. The 

 lines and the dots, when viewed with a power of 1000 linear, do not 

 seem to be precisely in the same plane, the latter appearing to be in 

 the membrane on the outer surface, and the former in that of the inner 

 surface of the vessel. When thus highly magnified, the dots exhibit 

 the same structure as in the similar but very much larger organs that 

 are so well known upon the dotted ducts of the Conferva ; having 

 the same lenticular form, and being furnished with a central area or 

 orifice, which is very apparent when the external surface of the vessel 



