1894.] On the Fossil Plants of the Coal-Measures. 119 



siderable tangential dilatation, allowing of a certain increase in the 

 diameter of the pith. 



The cortical tissues attained a great thickness in the older stems, 

 owing to the formation of abundant periderm. In one specimen the 

 first origin of the periderm, by tangential divisions of the inner corti- 

 cal cells, could be clearly traced. 



A periderm-like layer was also formed on the surface of the dia- 

 phragms, cutting them off from the medullary cavity. 



A number of specimens show the insertion of branches, on a rela- 

 tively main axis. The branches were placed immediately above the 

 node; often there were several in a whorl. Each branch usually 

 lies between two of the leaf-trace bundles next below. The pith of 

 the branch tapers towards the base, almost to a point, so that it is 

 connected with the medulla of the parent stem by a narrow neck of 

 tissue only. This gives rise to the characteristic conical form of 

 those medullary casts which represent the pith-cavity of the basal 

 portion of a branch. 



In favourable specimens the continuity of the primary wood of the 

 branch with that of the main stem can be demonstrated with 

 certainty. 



The branches were no doubt normal, not adventitious, appendages, 

 and arose near the growing point. Subsequently both the base of 

 the branch and the parent stem became coated by a common zone of 

 secondary wood. 



As the branch is traced, from below upwards, the diameter of the 

 pith becomes larger, the number of the vascular bundles increases in 

 the successive internodes, and the characteristic Calamitean structure 

 is assumed. At a certain distance above the base the dimensions 

 become approximately constant. 



Many of the branches were abortive, or were at least cast off at an 

 .rly age. This is proved by the fact that in many specimens the 

 pith of the branch is enclosed towards the exterior by the secondary 

 ood of the main stem. 



From specimens shown to one of us by M. Renault, it appears that 

 the roots, which were borne at or below the nodes, had the structure 

 of Astromyelon. This fact necessitates a re-investigation of the 

 fossils described under the latter name. 



2. Galamostachys. The homosporous C. Binneyana is first con- 

 sidered. 



The morphology of the strobilus is well known. The axis bears 

 ternate whorls of bracts and of sporangiophores. The bracts are 

 coherent for a considerable distance from their base, forming the hori- 

 zontal disc. Their free limbs turn vertically upwards, and extend at 

 least as. far as the second bracteal whorl above. The number of 

 bracts in each whorl is about 12. 



K 2 



