348 PROFESSOR W. C. WILLIAMSON ON THE PLANTS 



central punctuation has had no existence in the fossil 

 species, or it has disappeared in the process of fossilization : 

 I am unable to say which. It is certain, that in none of the 

 numerous sections of coniferous wood from the coal mea- 

 sures which have come under my notice, have I been able 

 to satisfy myself of its existence. 



In the section under consideration, the usual number of 

 vertical rows of disks on each fibre is two, but occasionally 

 there are three ; the average diameter of each disk being 

 about the — ^ of an inch. The fibres are readily detached 

 from each other. 



On making a section parallel with the bark, or at right 

 angles to the medullary rays, we have the structure deline- 

 ated in fig. 8, and still more highly magnified in fig. 9. 

 No disks exist on this surface of the pleurenchyma; but 

 along the line of junction of each two contiguous fibres, 

 there are a number of transverse bars (fig. 8 a and 9 a). 

 These appear to be the lines of division between different 

 disks ; since both in size and position they correspond ex- 

 actly with the areolae. Professor Balfour describes these 

 disks as " concave depressions on the outsides of the walls 

 of contiguous tubes, which are closely applied to each other, 

 forming lenticular cavities between the vessels, like two 

 watch-glasses in apposition."* The appearances presented 

 by fig. 9, seem to corroborate this interpretation. 



At fig. 8 d, are the intersected medullary rays, consisting 

 of single layers of superimposed cells. This characteristic 

 identifies the specimen with the first of M. Brongniarl's 

 subdivisions of fossil coniferous woods. The lateral aspect 

 of the medullary rays is represented in fig. 6 d; where the 

 section has been ground very thin, these rays are seen to 

 consist of the ordinary form of mural tissue. 



The structure of the entire woody zone bears a very 

 close resemblance to that of the Dadoxylon Brandlingi, 



* Manual of Botany, London, 1849. 



