TRANSACTIONS OF SECTION K. 849 



2. On II Primitive Type of Structure in Calamites. 

 By D. H. Scott, M.A., Ph.D., F.R.S. 



I'iilaiontological research lias afforded evidence that the Horsetails and Faco- 

 pods — groups now so distinct— had a common origin. The class Sphenopliyllales, 

 restricted, so far as we know, to the Pal;eozoic epoch, combines in an uumiEtakable 

 manner the characters of Equisetales and Lycopodiales, while at the same time 

 presenting peculiar features of its own. Broadly speaking, it is in the external 

 morphology find in the reproductive structures that the Equisetales are 

 approached, while the anatomy has an evidently Lycopodiaceous character. 



The synthetic nature of the Sphenophyllales, indicated clearly enough in the 

 type-genus Sphenophyllmn itself, comes out still more obviously in the new genus 

 Cheirodrobu^. Ilere the general morphology of the strobilus, the form and 

 structure of the sporangiophores and of the sporangia themselves are all of 

 a Calamarian type, while the anatomy of the axis is as clearly Lycopodiaceous in 

 character. 



So far nothing has been found to bridge the gulf which separates the anatomy 

 of the Oalamariete (Palaeozoic Equisetales) from that of the Spheuophyllalea or 

 the Lycopods. The most ancient known genus of Calamarieas — Arclueocalamite^ 

 ■ — approaches the Sphenophyllales in the superposition of the foliar whorls and 

 in the dichotomous subdivision of the leaves, points on which Professor Potonie, 

 especially, has laid stress. Anatomically, however, according to the researches of 

 Dr. Renault and Count Solms-Laubach, it was an ordinary Calamite, diflering ia 

 no essential respect from those of the Coal-measures. The stem oi Archa'ocalcanites, 

 like that of its later allies, had a large pith, surrounded by a ring of collateral 

 vascular bundles, the wood of which, primary as well as secondary, was wholly 

 centrifugal in development, the first-formed tracheides lying on the border of the 

 pith, at the points marked by the carinal canals. In Sp]te7iijphylliun, on the 

 other hand, the whole of the primary wood was centripetally developed, and there 

 was no pith. In Cheirostrobu^ the same holds good, except that an insignificant 

 portion of tlie primary wood may possibly have been added in a centrifugal 

 direction. In Lycopods there may or may not be a pith, but the whole 

 {Lycopodium, Psilotum, Lepidodendron) or the greater part {Tmesiptcris) of the 

 primary wood is centripetal. 



The Calamite which forms the subject of the present communication occurs in 

 the well-known Burntisland beds of the Calciferous Sandstone Series, at the base 

 of the Carboniferous Formation. The material is calcified, and the structure 

 excellently preserved, though the specimens so tar discovered are small and 

 fragmentary. Their interest depends on the fact that each vascular bundle 

 possesses a distinct arc of centripetal wood on the side towards the pith. The 

 carinal canals are present, as hi an ordinary Calamite, and contain, as usual, the 

 remains of the disorganised protoxylem. They do not, however, as in other 

 Equisetales, form the inner limit of the wood, but xylem of a considerable 

 thickness, and consisting of typical tracheides, extends into the pith on the inner 

 side of the canal, which is thus completely enclosed by the wood. Hence, starting 

 from the spiral tracheides of the protoxylem, there was here a considerable 

 development of xylem in a centripetal as well as in a centrifugal direction. That 

 the organ was a stem, and not a root, is proved, not only by the presence of the 

 carinal canals, but by the occurrence of nodes, at which the outgoing leaf-traces 

 are clearly seen. 



This appears to be the first case of centripetal wood observed in a Calamarian 

 stem, and thus serves to furnish a new link between the Palreozoic Equisetales and 

 the Sphenophyllales, and through them with the Lj'copods. 



The specimens have not as yet supplied any evidence as to the superposition or 

 alternation of the verticils, so we are not at present in a position to determine the 

 genus to which they belonged. Provisionally, until further investigation has 

 cleared up this question, the new stem may bear the name of Calamites petty- 

 curen&is, from the locality where it occurs. 



