Seward. — On the genus Myeloxylon (Brong.). 3 
mineralization. The tracheids are described as scalariform 
and reticulate. In conclusion Goeppert refers Myeloxylon 
elegans to those plants which must be looked upon as proto- 
types or synthetic types ; he recognises Ferns, Gymnosperms, 
and Monocotyledons as represented in certain structural details 
of this palaeozoic species. 
Binney 1 , in 1872, refers to Medullosa elegans of Cotta as 
the rachis of a Fern or of a nearly-allied plant. 
In 1873 2 Williamson refers the same plant to the Ma- 
rattiaceae : Schimper, on the other hand, classes Myeloxylon 
with the Cycads. 
In 1 876 3 Renault contributed an important paper in which 
a number of silicified specimens of Myeloxylon [Myelopteris 
of Renault, Stenzelia of Goeppert) from Autun and Saint 
Etienne are figured and described in detail. 
Several of the French specimens are much larger than 
any found in English rocks. The vascular bundles, which, 
especially in the small petioles, are arranged in fairly con- 
centric lines, Renault describes as consisting of large scalari- 
form vessels with smaller barred and spiral tracheids : the 
vacant space, which occurs in each bundle next to the group 
of xylem-elements, is referred to as a gum-cavity. In Plate 
IV. Fig. 37, one of these spaces is shown containing several 
cells or ‘ tubes ’ with their walls considerably thickened ; these 
are certainly not such elements as one would expect to find 
forming part of the phloem which originally occupied the 
vacant spaces in each bundle. Probably these so-called gum- 
cells with thick walls have found their way into the cavity left 
by the decay of the phloem. In a later work, Renault 4 makes 
no mention of the thick-walled cells, and speaks of the bast- 
part of the bundles as nearly always absent. Certain varia- 
tions in the arrangement of the hypodermal prosenchyma have 
1 Binney, Proc. Lit. and Phil. Soc. Manchester, vol XI. 
2 In a communication to the Brit. Assoc, meeting at Bradford. 
3 Renault, Recherches sur les vegetaux silicifies d’Autun — etude du genre 
Myelopteris (Mem. par divers savants; Acad, des Sci., Instit. de France, 
vol. XXVII [1876]). 
4 Cours de botanique fossile, vol. III. p. 162 (1883). 
