OF THE WOODY ZONE IN CALAMITE. 163 



the example figured being the only one of its kind 

 that I have either seen or heard of during thirty years 

 of association with the plants of the coal-measures. These 

 radii appear to have been composed of the same tissue 

 as the medulla itself^ judging from the circumstance that 

 the inorganic material with which they are filled is 

 identical with that replacing the pith"^ ; they have most 

 probably united the pith with the bark. As this func- 

 tion was amply performed by means of the medullary 

 rays in the fibrous tracts^ we must assume that the 

 radii had in addition some undiscovered special func- 

 tions of their own. On turning to the tangential section 

 (fig. 6), we find that a radius (6/) penetrates the centre 

 of the upper extremity of each cellular tract {d)y in which 

 portion it will be remembered there are no true medullary 

 rays — a circumstance which indicates that the prosenchy- 

 matous tracts are not merely prolongations of the pith, 

 since true prolongations of the latter passing through them 

 have retained their separate forms. Each radius is cylin- 

 drical_, somewhat compressed laterally, and occasionally, 

 but not often, rather triangular. In figs. 10/ and 17/ 

 we see its position in reference to the node of the woody 

 zone, having a mass of vascular tissue (c) above, and the 

 prosenchymatous tissue [d) below it. A very limited 

 portion of the latter tissue, peculiarly deflected, interposes 

 between the upper surface of the radius and the remarkable 

 articular or nodal arrangement of the vascular elements 

 next to be described. 



It must be remembered that the longitudinal grooves of 

 Calamites usually alternate in contiguous joints or inter- 

 nodes, the elevated ridges of one joint being continuous 



* My friend Mr, Carruthers has suggested that the sears left when these 

 radii are broken off represent the openings of meshes in the woody tissue 

 through which vascular bundles passed to whorls of leaves or branches 

 produced at the nodes (Geol. Journal, July 1868, p, 332) ; but my specimens 

 do not sustain this opinion for the reasons given in the text. 



M 2 



