III. On the structure and affinities of fossil plants from the palæozoic rocks.—III. On medullosa anglica , a new representative of the cycadofilices

Abstract

For some years past the existence of a group of fossil plants, combining in their organization certain characters of Ferns and Cycads, has been recognized by several Palæobotanists. Potonié, in his new “Lehrbuch der Pflanzenpalæontologie," has proposed the convenient name Cycadofilices for this group, in which he includes the genera Nœggerathia, Medullosa, Cladoxylon, Lyginodendron, Heterangium , and Protopitys . Among these the genus Medullosa , with its allies Colpoxylon , Brongn., and Steloxylon , Solms, is by no means the least remarkable. The large stems, reaching half a metre in diameter, have an extraordinarily complex-structure, containing a system of numerous vascular rings, of the most various dimensions and shapes, each ring growing in thickness by a cambium of its own. The structure bears, at first sight, a striking resemblance to that of the anomalous Sapindaceæ, with which it was compared by Goeppert and Stenzel, but more recent writers have found a better analogy in the organization of a polystelic Fernstem, each stele, in the case of the Medulloseæ, having its own zone of secondary growth, a condition not known among recent plants. The general character of the secondary tissues, and the anomalies presented by certain of the older stems, are strongly suggestive of Cycadaceæ, though the ground plan of the structure is rather that of a Fern.