38 STIGMARIA FICOIDES. 



have disappeared or are disappearing, are innumerable, and have no specific 

 signification. The above figure is half the size of the original. 



Plate XII, fig. 72. A cast of the outer surface of a small fragment of Stig- 

 marian bark in which the spaces between the rootlet-scars are occupied by still more 

 strongly marked undulating longitudinal lines. This seems to be the condition to 

 which Goeppert gave the name of Stigmaria unclulata. The original is in the 

 Museum of the Owens College. I have seen similar specimens with corresponding 

 undulation, but so faintly preserved as to show that they merely represent another 

 of the variable conditions of preservation just referred to. 



Plate XIV, fig. 73, is a Stigmarian fragment displaying the more normal 

 conditions of the rootlet-scars ; they are depressions, disposed in diagonal lines, 

 producing what is known as the quincuncial arrangement. The large central 

 cavity, b, is, like that of Plate XIII, fig. 65, the result of the disappearance of the 

 vascular cylinder from its medullary interior. 



Plate XII, fig. 74, is a small fragment of Stigmarian bark from near Oldham, 

 represented of the natural size. Since the tissues of the outer bark as well as of 

 the bases of the rootlets occupying the bottoms of the sunken scars are preserved 

 in this specimen, it becomes instructive, teaching the true histology of those 

 depressed scars, and showing how the rootlets themselves have disappeared. At 

 the outer margin, g, of each of these depressions we see the remains of the outer- 

 most or cortical zone of the base of each rootlet. Within this outer circle we have 

 the still deeper depression, h, produced by the disappearance of the second delicate 

 parenchyma, g', of Plate IX, fig. 51. At the bottom of the latter depression we see 

 traces of the apex of the rootlet cushion, li. Specimens like this clearly show 

 that there has been no kind of " articulation " where the rootlet was planted upon 

 the bark. There was no definite plane corresponding to the cicatrix left by a 

 fallen leaf at which the rootlet separated from the bark. The separation was the 

 result either of external force or of decay, producing a variable contour in what 

 remained of the torn tissues of the rootlet. The rootlets of the living Isoetes lacustris 

 illustrate this tendency to detachment by rupture, as contrasted with dis- 

 articulation. 



Plate XIV, fig. 75, is an unusually fine specimen, from the neighbourhood of 

 Newcastle-upon-Tyne, for which I am indebted to the kindness of Professor 

 Lebour. Similar examples have been figured both by Sir Joseph Hooker 1 and by 

 Mr. Binney, 2 but both these authors have fallen into the same error in their inter- 

 pretations of their specimens. Each of them supposed that the surface which he 

 figured was the true exterior of the bark, whereas it was exactly the reverse ; it 



1 Memoirs, ' Geol. Survey of Great Britain,' vol. ii, part ii, pi. ii, figs. 1, 2, and 3, 1848. 



2 ' Carboniferous Flora,' part iv, Sigillaria and Stigmaria, pi. xxiv, fig. 1, Palaeontographical 

 Society, 1875. 



