90 



On the Fossil Plants of the Coal-measures. 



[Dec. 19, 



sected at intervals of nearly ^ of an inch by horizontal and parallel 

 bands of very dark-coloured cells of a special nature. 



Seven or eight large vasculo-cellular bundles exist in each transverse 

 section of the bark. Some of these are located within the exogenous 

 layer of the wood, being obviously detached portions of the cells and vessels 

 of the medullary axis ; others occur, in various specimens, at every point 

 between the wood and the outer bark. The author finds that these 

 bundles remained for a time in the immediate neighbourhood of the inner- 

 most bark, but that they successively became detached and moved more 

 rapidly outwards, until each one emerged at the periphery of the bark in 

 one of the prominent angles of the latter, already referred to ; when one 

 bundle has thus reached the periphery, another begins to follow the same 

 centrifugal course. The inference is, that these are foliar bundles, sup- 

 plying large leaves or petioles, sparsely grouped round the stem. A single 

 example of a similar centrifugal bundle was found in D. Oldhamium. 

 The seemingly irregular projections of the bark of D. Grievii thus appear 

 to represent angular petioles, and are not the result of merely accidental 

 pressures. A second kind of cylindrical bundle is noticed, consisting of 

 reticulated prosenchymatous cells. It is connected at its central extre- 

 mity with the medullary parenchyma, whilst its peripheral end passes out- 

 wards through the bark. It appears to have had the same character as 

 the similar one of D. Oldhamium, having probably been an adventitious 

 root-bundle. 



Somewhat triangular twigs or petioles of the above plant are numerous. 

 They consist of a single vascular bundle, located excentrically near the 

 cordate base of the triangular transverse section, and surrounded by the 

 three bark-layers seen in the older stems. The structure of these layers, 

 as seen in the longitudinal sections, is identical with, though less com- 

 plex than, that of the matured stems ; but no cortical vascular bundles 

 are seen in them. 



Having identified his Didyoxylon Oldhamium with the older genus Ly- 

 ginodendron, the author abandons his own generic name, and proposes that 

 the plant shall henceforth be designated Lyginodendron Oldhamium. He 

 establishes in the same way the generic identity of Dictyoxylon Grievii 

 with the Heterangium of Corda ; hence that plant must now take the name 

 of Heterangium Grievii. Whilst having no doubt that the above were two 

 Cryptogamic plants, it appears impossible for the present to determine to 

 what class of Cryptogams they belong. Many of their features indicate 

 Lycopodiaceous affinities ; but this point can scarcely be determined until 

 the actual fronds are discovered. This has not yet been done. The 

 Lyginodendron is from the horizon of the Granister beds of Lancashire and 

 Yorkshire ; the Burntisland deposit belongs to the middle portion of 

 the calciferous sandstones of the Burdiehouse Carboniferous strata. 



