362 REMAINS OF STEMS OF DOUBTFUL AFFINITY, ETC. 



differences in character between the central cylinder inclosed within the 

 ring of wood, and the same cylinder as known in Cycadeae. All these 

 things considered, I abstain from expressing an opinion one way or the 

 other with respect to the affinities of these remains. Renewed investigation 

 will no doubt throw more light upon them. Into speculations respecting 

 certain groups intermediate between Ferns and Cycads which might readily 

 be connected with the present subject, I do not propose to enter here 

 any more than in other places in this work, which would have been suitable 

 for them ; the reader will find no difficulty in forming such an idea of them 

 as may be needful from the facts here given, and they will not fit into the 

 frame of such an account of our subject as was intended in the present work. 



Corda l has described as Heterangium paradoxum a very imperfect bit 

 of stem from the sphaerosiderites of Radnitz in Bohemia. It is nothing but 

 some shreds of tissue, in which irregular groups of broad and narrow pitted 

 vessels are seen in the middle of a small-celled tissue which has been broken 

 up and disintegrated. Williamson subsequently recognised in these remains 

 some fragments of the central strand of a stem which he had obtained 

 in section from the infra-Carboniferous calcareous nodules of Burntisland, 

 and which he accordingly named Heterangium Grievii 2 . I have received 

 another and similar species through Cash's kindness, which was obtained by 

 Mr. Binns at Halifax from the Lancashire nodules ; it will probably be 

 soon and fully described by Williamson. The identification with Corda's 

 specimen may be taken to be perfectly satisfactory; at all events I cannot 

 sympathise with the doubts expressed by Renault 3 , which are founded on 

 too strict an interpretation of Corda's statements. 



We shall have an idea of the structure of the stem in Heterangium 

 Grievii, W T ill., if we imagine the central portion in a stem of Lyginodendron 

 to be occupied by a uniform closed primary vascular bundle, with its tracheal 

 elements in irregular groups and irregularly imbedded in a fundamental 

 parcnchymatous tissue. The surrounding secondary wood is less strongly 

 developed than that of Lyginodendron, but is like it in all other respects. 

 All the tracheal elements have bordered pits. The thick parenchymatous 

 rind is traversed by leaf-traces which are here formed of one strand only ; 

 these bundles Williamson in this case accepts as leaf-traces, though they 

 ascend almost as steeply as the analogous bundles in Lyginodendron. The 

 outer hypodermal Dictyoxylon-layer is narrower than in Lyginodendron, 

 but its fibre-plates are more crowded together and of larger size. The 

 inner layer is formed of compact parenchyma, in which transverse lines of 

 darker cells may be seen on the radial section following one another at 

 regular distances. 



But the systematic position of Heterangium still remains doubtful, 



1 Corda (1), p. 22, t. 16. * WilHamson (1), iv, p. 394 ; tt. 28-31. 3 Renault (1), p. 277. 



