372 ARTHUR /. MASLEN [may 



Most of these types have been put into the class Meclulloseae, 

 some of the forms belonging to which were, in the very early clays of 

 palaeontology, regarded as Carboniferous palms. Mr. A. C. Seward, in 

 a paper on Mydoxylon 1 (now known to be petioles of Medullosa) points 

 out that Corda thought it a palm, and Brongniart a doubtful 

 monocotyledon ; but the researches of Goeppert, Williamson, Weber, 

 Sterzel, and others have shown that the affinities are both cycadean 

 and filicinean. On the whole, Mr. Seward concludes that the fossil 

 specimens are related more nearly to the cycacls than to the ferns. 



Sterzel and 0. Weber" made a very important addition to 

 our knowledge of the Meclulloseae by proving that these petioles 

 {Mydoxylon) were borne on stems of Medullosa. The petioles in 

 transverse section exhibit a large number of vascular bundles encased 

 in a mass of parenchyma, each separate bundle being collateral and 

 having the protoxylem placed on the side turned towards the phloem, 

 the xylem having therefore developed entirely in a centripetal 

 direction, an evidently cycadean character. Sterzel also regards 

 the Meclulloseae as having more affinities with cycads than with 

 ferns. 



The Medulloseae exhibit, in their stem, a type of structure 

 different from anything known among living plants, and probably 

 represent, as Solms-Laubach has suggested, a divergent branch which 

 has left no descendants among the existing vegetation. They range 

 from the Coal Measures to the Permian strata, and vary considerably 

 in the complexity of their internal stelar structure ; the outer surface 

 of the stem being, in most cases, unknown. 



The oldest and simplest known form of the genus, Medullosa 

 anglica, from the Lower Coal Measures of Lancashire, has been recently 

 described before the Koyal Society by Dr. Scott. 3 " These fossils are 

 of special interest on several grounds : they are considerably more 

 ancient than any members of the genus previously described ; they are 

 the first English specimens recorded ; they are preserved in a more 

 complete and perfect form than any others at present known ; and 

 lastly, the greater simplicity of their structure causes the essential 

 characters of the genus to stand out with greater clearness than in the 

 more complex species." In some of the specimens the habit of the 

 stem, clothed with overlapping leaf-bases, can be made out, and 

 appears to have been not unlike some of the tree-ferns, such as 

 Alsophila procera. 



The transverse section of the stem shows the presence of three or 

 four steles, each possessing a pithless xylem strand with the protoxylem 

 elements close to, but not actually at, the periphery (mesarch). Each 



1 Annals of Botany, 1893, vol. vii. 



2 Sterzel, J. T. D. " Beitrage zur Kenntniss der Meclulloseae. Nach Mitteilungen 

 unci alteren Abbildungeu von 0. Weber nachtraglich bearbeitet," Ber. Nat. Ges. Chemnitz. 

 (1896), xiii. pp. 44-143. 



3 See Nature (1899), vol. lix. p. 381. 



