252 PEOCEEDINGS 0¥ THE GEOLOGICAL SOCIETY. [March 24, 



is the result of his independent observations. Binney obviously 

 confuses the two kinds of horizontal structures when he speaks 

 throughout his papers of medullary rays composed of " finely barred 

 vessels.'^ He neither figures nor describes any true medullary ray ; 

 and it is certain from his drawing's that they do not exist. This I 

 have moreover established by the examination of numerous beauti- 

 fully preserved specimens. 



If, then, I am right in believing that the struct areless spaces in 

 the vascular cylinder of Sigillaria elegans do not represent medullary 

 rays, the structure of the stem exactly agrees with that of the root. 

 This is, moreover, precisely the structure of Lepidodendron, JIahnia, 

 Ulodendron, &c., so that I venture to refer, without any doubt, all 

 these genera to the same great group of extinct arborescent Lycopo- 

 diacece. 



Dr. Dawson describes the vascular cylinder of Sigillaria as much 

 more complex than anything I have seen. He says it was double, 

 the inner portion being composed of scalariform, and the outer of 

 discigerous vessels. He has figured a specimen of a stem in which 

 the two kinds of tissue exist together. The important discigerous 

 tissue could not be altogether wanting in Brongniart's specimen if 

 it were really a constituent part of the Sigillarian stem, even though^ 

 as Dr. Dawson suggests^, it were a young stem or branch *. 



* Since writing the abore I have had, through the kindness of Sir Charles 

 Lyell, the privilege of examining Mr. Daw^son's specimen of the Sigillaria figured 

 in plate 17, vol. "xv. of the Society's ' Quarterly Journal,' and which has supplied 

 him with the data for his interpretation of the internal structure of the genus. 

 It is unnecessary for me to say that the specimen is accurately figured and 

 described ; but it yet appears to me more than doubtful that it belongs to Sigil- 

 laria. The fact that it was found within the trunk of an erect Sigillaria is not 

 sufficient ; for we know that hoUow Sigillarice were often filled with foreign 

 materials. Dr. Dawson has himself obtained from trees at the Joggins, where he 

 found this specimen, the remains of a Lizard. In one of the stems from the 

 volcanic ash-beds at Ai'ran I have determined the existence of some eight or ten 

 distinct stems belonging to several genera. The stem of the Sigillaria was 

 erect ; and all these contained stems were arranged parallel to the stem itself. 



If the argument I have employed above is of any value, the axis described by 

 Dr. Dawson must be foreign to the Sigillaria in which it occurred, seeing it 

 contains structures which are not found in any of the numerous specimens of 

 Stigmaria that have been examined. The root and stem, being homological 

 structures, are in living plants composed of similar tissues. It is impossible to 

 conceive of another state of things existing. But in Dr. Dawson's axis there 

 are true medullary rays and true coniferous disk-bearing tissue, neither of 

 which occur in Stigmaria. I have no doubt that Dr. Dawson's fossil is a true 

 coniferous stem, having a large Sternhergia-^iih. hke some other carboniferous 

 Coniferce. The scalariform vessels occupy the position of the "medullary 

 sheath." Though true scalariform vessels have not been detected in the 

 Coniferce, they occur in the closely aUied Gymnospennatous order Cycadece. 

 The single series of disks on the walls of the vessels indicate an affinity between 

 this fossil and the Abietineous Conifers ; there are, however, other characters 

 which make it impossible at present to refer this and similar fossils with certainty 

 to any recognized group. I believe Dr. Dawson's fossil to be the same as a stem 

 which has for some time been engaging the attention of Prof. Wilhamson, for 

 which he has proposed the name Calamopiti/^ and a full description of which 

 may be early expected from him. 



