412 



Prof. W. C. Williamson on the 



[Nov. 15, 



numerous carboniferous plants whose vascular zone grew by exogenous 

 additions, yet the exclusion of every modification of tissue, except 

 barred vessels, from the vascular laminae suggests Cryptogamic rather 

 than Grymnospermous affinities. 



Astromyelon is the only distinct type of plant left undescribed in the 

 lecturer's previous Memoirs ; but he has obtained a considerable amount 

 of additional information respecting some of those previously examined. 



Catamites. — A description is given of a series of specimens, beginning 

 with very small twigs composed of parenchyma, which is only divided 

 into pith and bark by a ring of the internodal canals characteristic of 

 Calamites. The medulla is continuous and not fistular. Then follow 

 others in which very slight traces of vascular tissue are seen external to 

 each internodal canal, and which constitute the beginnings of a corre- 

 sponding number of vascular w r edges ; still higher in the series of sections 

 others are arrived at in which these vascular wedges are more fully deve- 

 loped ; the medulla has become fistular and the cortical cells are differ- 

 entiated into a coarser tissue than the medullary one. A Calamite of 

 much larger dimensions is then described, in which the fistular me- 

 dulla is enclosed within a large vascular cylinder, the component radiating 

 laminae of which are fully two iuches in length. Sections of this ex- 

 ample show 7 that the peculiar Calamitean features seen both in trans- 

 verse and tangential sections of all young specimens, and which features 

 are also very distinctly seen at the inner portion of the vascular zone of 

 the specimen described, almost wholly disappear towards its periphery. 

 The bark of this example has undergone marked development and differ- 

 entiation. There is an inner zone of parenchyma, passing quickly into a 

 thick middle one of prismatic cells, identical with the " couche subereuse " 

 of M. Renault, or corky layer seen in Lepidodendron and Sigillaria. This 

 has obviously not been the outermost layer of the bark ; the specimen 

 had been weather-worn. A series of additional facts are given, illustra- 

 ting the nature of what the lecturer has previously termed the intranodal 

 canals, and also the structure and arrangement of the branches given off 

 from the nodes. He shows that the young branches do not exhibit all the 

 peculiar Calamitean conformation until they have emerged from the vascular 

 zone of the parent stem ; whilst older ones develop a thick vascular zone, like, 

 and continuous with, that of the parent stem. Hence he concludes that 

 the minute specimens already referred to in which the internodal canals 

 exist, but have few or no vascular bundles associated with them, are pro- 

 bably not branches, but young plants developed directly from spores. 



The lecturer again points out the extreme improbability that two genera 

 belonging to t} r pes so widely apart from each other as the Grymnosper- 

 mous Exogens and the Cryptogainous Equisetacese should exhibit such 

 minute organic resemblances as obviously exist between the supposititi- 

 ously separate geneia Calamodendron and Catamites. Eurther it is to be 

 remembered that, notwithstanding the extreme abundance of the supposed 



