1882.] Organisation of Fossil Plants of the Coal-measures. 33 



-described by Corda, and which, leave no room for doubting that our 

 British Coal-measures contain at least one arborescent fern, equal in 

 magnitude to those obtained from the deposits at Autun. 



In his Memoir, Parts IX and X, the author described under the 

 provisional generic name of Zygosporites, some small spherical bodies 

 with furcate peripheral projections. Similar bodies had been met 

 with in France, and were regarded by some of the French palaeontolo- 

 gists as true Carboniferous representatives of the Desmidiaceee. The 

 author was unable to accept this conclusion, deeming it much more 

 probable that they would prove to be spores of a different kind. 

 Mr. Spencer exhibited the specimen now described at the York meet- 

 ing. It is a true sporangium, containing a cluster of these Zygo- 

 sporites. Though they undoubtedly bear a close superficial resemblance 

 to the zygospores of the Desniidiae, their enclosure within a common 

 sporangium demonstrates them to be something very different. There 

 is now no doubt but that they are the spores of the strobilus described 

 by the author in his Memoir, Part V, under the name of Volkmannia 

 Dawsoni. Hence the genus Zygosporites may be cancelled. 



Another interesting specimen found by Mr. Wild is a young 

 Calamite, with a more curiously differentiated bark than any that 

 has hitherto been discovered. The structure of the vascular cylinder 

 and of the innermost layer of the bark differs in no essential respect 

 from those previously described ; but the outermost portion displays 

 ;an entirely new feature. It consists of a narrow zone of small longi- 

 tudinal prosenchymatous bundles, each one having a triangular sec- 

 tion, the apex of each section being directed inwards, whilst their con- 

 tiguous bases are in contact with what appears to be a thin epidermal 

 layer. As in every previously discovered Calamite in which the cortex 

 is preserved, the peripheral surface of this specimen is perfectly smooth 

 or " entire." It displays no trace of the longitudinal ridges and furrows 

 seen in nearly all the traditional representations of Calamites figured 

 in our text-books. 



It has long been seen that the medullary cells of the Lepidodendra, 

 as well as the vessels of their non-exogenous medullary sheaths, steadily 

 increased in number as these two organs increased in size correlatively 

 with- the corresponding general growth of the plants. But the way in 

 which that increase was brought about has continued to be a mystery. 

 The author now describes a Lepidodendron of the type of L. Harcourtii 

 in which nearly every medullary cell is subdivided into two or more 

 younger cells, showing that, when originally entombed, the pith was 

 an extremely active form of meristem, though the branch itself had 

 attained to a diameter of at least two inches. The numerous small 

 young cells are of irregular form. Their development by further 

 growth into a regular parenchyma would inevitably necessitate a 

 •corresponding increase in the diameter of the branch as a whole; 



VOL. XXXIV. D 



