Royal Microscopical Society. 53 



tion of Lepidodendron, proposes to call this axis a medulla* Our 

 specimen clearly establishes that this cannot be the nature of the 

 axis. It is, as we have said, entirely composed of scalariform 

 tissue; it gives off from its outer surface the vascular bundles 

 which supply the leaves ; it has no investing scalariform or woody 

 tissue, and it is placed in the centre of the cellular tissue of the 

 stem. There can be no doubt that it is homologous with the 

 vascular axis of the hving Lycoimliacege, as Witham, in the first 

 paper that treated of the internal structure of a Lepidodendron, 

 with remarkable sagacity suggested.! The circumference of the 

 axis is precisely similar to*^ that oi Lepdodendron Harcourtii, With., 

 being entirely without any investing cyhnder ; but in that species, 

 as figured by Witham,t by Lindley and Hutton,§ and by Brongniart,|l 

 the interior of the axis is composed of " elongated cellular tissue " 

 (Brongn.), with acute terminations, and having a scalariform 

 structure. There is no indication of such a change in the structure 

 of the axis of this plant either in the transverse or longitudinal 

 section. 



The tissue surrounding the axis, PI. VII., Figs. 3h, 4fc, has 

 completely perished in the specimen figured, and the space which it 

 occupied is filled with semi-transparent carbonate of lime, except 

 when here and there a leaf bundle has resisted decay. The de- 

 stroyed tissue, which is well preserved in some specimens that I 

 hope to figure in due time, was a thin-walled parenchyma. 



Beyond this, PL YII., Figs. 3 c, 4 c, are the true epidermal 

 tissues of the stem. The spherical cells have thickened walls. 

 They are of larger size towards the interior of the stem, and the 

 smaller cells of the exterior are found in longitudinal section to be 

 slightly elongated, yet not to so great an extent as in Lepidoden- 

 dron selaginoides, Sternb.lF This epidermal layer has successfully 

 resisted decay. Scattered through it are several leaf bundles m 

 open spaces apparently completely detached from the tissue itself. 

 This isolation has been produced by the decay of the dehcate cel- 

 lular tissue which accompanied the bundles from the inner perishable 

 layer. Stems frequently occur, especially in arenaceous rocks, in 

 which the hollow interior has been filled in with the amorphous 

 substance of the rock, and this has pushed itself from the interior 

 outwards through the empty passages occupied by the cellular 

 tissue of the leaf bundles. The indurated epidermal tissues having 

 been subsequently converted into coal, and removed, by slow com- 

 bustion before the specimen was taken from the rock, or by accident 



* ' Proc. Eoy. Soc.,' vol. xix., p. 500. 



t ' Trans. Nat. Hist. Soc.,' Newcastle-on-Tyne, March, 1832. 

 ' X I. c, PI. ii., figs. 2 and 4. 



§ ' Fossil Flora,' PI. xcviii., fig. 2. 



II ' Observ. Sigillaria elegans,' PI. xxx., figs. 5, 8 ; xxxi., fig. 4. 



i 'Mod. Micr. Journ.,' 1869, PI. XXVII., Fig. 2e. 



