The Royal Seciety, London. 41 



of smaller bundles, each of which lias collateral structure. These 

 collateral Strands have in all respects the same arrangement of their 

 Clements as the well known bundles of Myeloxylon. 



The base of the leaf received a large number of bundles, 

 consisting of the ultimate branches derived from the subdivision of 

 several of the original leaf-traces. This distribution of the bundles 

 is peculiar and unlike that in any known plants of Cycadean 

 affinities. 



In a few cases accessory vascular Strands, of concentric stueture, 

 recalling the cortical bundles of a Cycas, were found to the outside 

 of the normal stelar systera. 



The stem formed a well marked zone of internal periderm. 

 In one specimen the wliole of the outer cortex, with the leaf-bases, 

 Lad been exfoliated, so that in this case the periderm formed the 

 externa! surface. 



The leaf-bases and petioles present in all respects, as regards 

 hypoderma, vascular bundles, and gum-canals, the characters of the 

 Myeloxylon Landriofü of Renault, which was evidently not a species, 

 but a type of leaf stalk common to various MeduUosae. The petioles 

 branched repeatedly, the finest ramifications of the rachis having 

 a diameter of about 1 mm. only, but retaining in essentials the 

 "Myeloxylon" structure. The leaf was thus a highly Compound one; 

 the structure of tlie leaflets associated with the rachis, agrees well 

 with that of the Ahthopteris leaflets, figured by M. Renault. 



The roots, never previously observed in any species of Medullosa, 

 were of triarch structure, with abundant formation of secondary 

 wood and hast, and an early development of internal periderm, 

 by which the primary cortex was thrown off. Developmental 

 stages show that the periderm originated in the pericycle. The 

 roots, which branched freely, were borne on the stem in vertical 

 series, between the bases of the leaves. They were attached to 

 pedicels, through which the vascular tissues of the roots were 

 continuous with those of the stem. The author is indebted to 

 ]\Ir. J. Butterworth and Mr. G. Wild, for speciraens which 

 have thrown important light on the connection between root and stem. 



The füll paper concludes with a short historical resume, and 

 a discussion of affinities. 



Medidlosa anglica, in the structure of its stem, shows unmista- 

 kable affinities with Heterangium, perhaps the most fern-like of the 

 genera grouped under Cycadofilices. The new species is far simpler 

 tiian any Medidlosa hitherto described, for the steles are not only 

 few but are uniform, showing now differentiation into a pheripheral 

 and a central System. The small central steles, called "Star-rings" 

 in other Medidlosae. are absent here. In these and other points 

 he species agrees wath the genus Colpoxylon of Brongniart, 

 but as that genus is doubtfoully distinct and its leaves are not 

 known, it is not proposed to unite the English species with it. 



In the structure of the petiole and of the leaf generally, 

 Medidlosa anglica is a highly organised as any of the MeduUosae^ 

 and agrees closely with M. Leuckarti, the only other species in 



