LEPIDODENDREAE. 227 



Witham's original specimen figured in Lindley and Hutton *, and in Brong- 

 niart 2 is merely the ordinary cast without the rind. The specimen with a 

 Bergeria-surface figured in Binney 3 as Lepidodendron Harcourtii is struc- 

 tureless up to the central strand, which is in the act of dividing, and is filled 

 with clay-ironstone ; it cannot therefore be taken into consideration here, 

 though from the structure of the xylem-strands it is probable, if not quite 

 certain, that it has been correctly determined. We know therefore only 

 the middle and inner cylinders, which are both of great thickness and 

 consist entirely of parenchyma. The growth in thickness appears in this 

 case to be much less localised ; notwithstanding the great thickness of the 

 rind, the periderm is much less developed and not nearly so conspicuous 

 as in the previous type. But while in Lepidodendron Williamsoni these 

 two cylinders, which differ little in the character of their tissue, are both 

 as a rule in a like state of preservation and are not distinctly separate from 

 one another, in the other species on the contrary the inner cylinder is more 

 or less destroyed in my specimen entirely destroyed up to the leaf-trace- 

 bundles by which it is traversed, while the outer, consisting of thick- walled 

 parenchyma, is remarkably well preserved. The consequence is that the 

 two species can be distinguished at first sight in a preparation. The 

 behaviour also of the central bundle in the formation of lateral branches is 

 known in the case of the type of Lepidodendron Harcourtii, and has been 

 figured by Williamson 4 . The strand divides exactly as in the formation 

 of a dichotomy, only the two parts are not of equal size, as they are in the 

 latter case, which has been observed in Lepidodendron vasculare. A small 

 segment in the form of a portion of a flat arch separates from the circular 

 tracheid-zone of the bundle, so that the remaining portion is seen to have 

 an aperture on one side and to be in the form of a horse-shoe. The small 

 opening thus formed soon closes again above, and thus forms a longish 

 lateral slit in the tracheal tube, through which the central parenchyma of 

 the strand enters into communication with the rind. The process was 

 observed to be exactly the same in the normal bifurcation of the vasculare- 

 type, only there the opening was at the top of the basal piece in the angle 

 of the dichotomy. The two cases are accordingly distinguished only by 

 the lateral displacement connected with the formation of a sympodium. 



Various previously described remains with imperfectly preserved inner 

 structure appear from the statements of authors to belong to the type of 

 Lepidodendron Harcourtii. Lepidodendron nothum and L. Richteri 5 

 from the Cypridinae-schists (Upper Devonian beds) of Saalfeld may be 

 first mentioned, and after them L. squamosum G from the Carboniferous 

 Limestone of Glatzisch-Falkenberg, in which the form of the central 



1 Lindley and Hutton (1), vol. ii, t. 98. 2 Brongniart (7), t. 30. 3 Binney (1), in, t. 14, f. I. 

 Williamson (1), xi, t. 52. 5 Unger (5), tt. 10, n. 6 Gb'ppert (12), tt. 21, 22. 



Q 2 



