356 DR D. H. SCOTT ON THE 



that presented by the tangential section of Lyginodendron anomalum (Williamson, 

 loc. cit., fig. 92), except that in the latter the dilated medullary rays are on a still larger 

 scale. 



In Pitys primseva the dilated rays are limited to the neighbourhood of the lateral 

 branch, becoming normal at a greater distance from it. 



The puzzling structure of Lyginodendron anomalum, which is only known as a 

 fragment of calcified wood from the volcanic ash of Arran, was correctly interpreted by 

 Williamson, who says (I.e., p. 352) : " These cell-masses are in fact huge medullary 

 rays of a most extraordinary form." No stem, however, has hitherto been known, 

 presenting the same peculiarity in so extreme a degree. Mr Seward, who observed a 

 somewhat similar enlargement of the rays near the outgoing leaf-trace, in the stem 

 named by him Lyginodendron robustum, made the following suggestion : " Such a 

 comparison suggests the probability that the shorter and broader medullary rays and 

 the more irregular course of the tracheides may not represent the normal character of 

 the stem from which the Arran fragment was obtained, but that these appearances may 

 be the result of some disturbing influence in the secondary wood." * In the specimen 

 of Pitys primseva just described, we have a striking confirmation of Mr Seward's 

 suggestion. Under the ' disturbing influence ' of the presence of a lateral branch, the 

 wood of this plant assumes the same peculiar structure which characterises the Arran 

 fragment, while elsewhere retaining the ordinary organisation. 



In other respects, and notably in the pitting of the tracheides, there is a close, 

 though not an absolutely exact agreement between the wood of Pitys primseva and 

 that of the Arran fossil, which is of similar Lower Carboniferous age. It is possible 

 that the two are specifically identical, the specimen known as Lyginodendron anomalum 

 being simply a fragment of a large stem of Pitys primseva, from a part affected by the 

 presence of some bulky appendage. Until further evidence is obtained, it may be well 

 to keep up Williamson's specific name, but the genus is presumably Pitys rather than 

 Lyginodendron. 



The Genus Pitys. 



Apart from the doubtful fragment last mentioned, all the species of Pitys, as limited 

 by GoEPPERT,t prove to be characterised by the presence of small primary strands of 

 xylem around the pith. Goeppert enumerates four species, P. Withami, P. medullaris, 

 P. antiqua, and P. primseva. The first two are not really distinct,J and the name 

 medullaris therefore disappears from the list. The remaining three, P. Withami, P. 

 antiqua, and P. primseva, have all been found to possess the primary xylem-strands, 

 which I propose to make a character of the genus. 



* Seward, "A Contribution to our Knowledge of Lyginodendron," Ann. of Bot., vol. xi. p. 81, 1897. 



t Goeppert, " Revision meiner Arbeiten liber die Stamme der f ossilen Coniferen, etc.," Bot. Gentralbl., Bd. v., 1881, 

 p. 403. 



J Goeppert, I.e., p. 404, conjectures that all four may have to be united. This, however, is not borne out by 

 comparison of the specimens ; P. prim&va is a very distinct form, and P. Withami and P. antiqua, though allied, 

 are not identical. 



