226 LEPIDODENDREAE. 



distinguish species with any certainty, that of Lepidodendron Harcourtii, 

 With, is represented by two well-defined species. One of these appears to 

 be very rare, and to it belongs the stem first discovered by Witham. It is 

 only quite recently that we have succeeded in obtaining further specimens 

 of it, and I am indebted to Mr. Cash's kindness for a transverse section of 

 one of these. The other species, which is tolerably plentiful in Lancashire, 

 was in the meantime examined repeatedly by Williamson and Binney, but it 

 was not distinguished from the first species and went by the same name. 

 We will call it here Lepidodendron Williamson! (L. Harcourtii, Will. 

 ex pte, not With.). The preponderating development of the parenchy- 

 matous cortex is much more striking in the Harcourtii -type than in that of 

 L. vasculare ; as compared with it the central strand is still more insigni- 

 ficant. There is usually no secondary growth in thickness, or else it appears 

 in a feebly developed and rudimentary form, and on one side only of the 

 periphery of the central xylem-strand. The latter separates into a central 

 pith-like purely parenchymatous cylinder entirely without tracheides, and this 

 is surrounded by a closed ring of tracheal elements which is sharply defined 

 on its inner side, while its outer boundary is rendered sinuous in a peculiar 

 manner by the presence of numerous small sharp teeth, which correspond 

 to the sections of the points of attachment of the strongly decurrent leaf- 

 traces. The transverse sections of these bundles, which have already set 

 out from the central cylinder, and which agree in all important points of 

 structure with the trace-bundles of the vasculare-type, lie in the sinuses 

 and are inclosed in delicate tissue. There is this difference between the two 

 species, that the small teeth in the boundary-line of the central strand project 

 much more sharply and are also longer in Lepidodendron Harcourtii than in 

 L. Williamsoni. A further difference is that the trace-bundles of the former 

 species contain a group of bast-fibres which is wanting in those of the 

 latter. Hence in the one case the bundles in their course through the 

 rind appear under the lens to be made up of two brown points, in the 

 other to be single. The inner one of these two points consists of well- 

 preserved tracheides, the outer is less distinct, and it is only in rare cases 

 that its cells can be certainly distinguished l . Between the two there is 

 always a gap, which was formerly filled with soft bast. Whether this bast 

 surrounded the wood -portion, in other words whether the bundle was con- 

 centric or collateral, must again be left undecided ; from the figure given 

 by Binney 2 we might almost suspect that it was collateral. But I have 

 not met with so well-preserved a bundle in the preparations which I have 

 examined. 



Of the rind, it is to be observed that its outer cylinder with the leaf- 

 cushions has never been found with the structure preserved ; for even 



Brongniart (7), t. 31, f. 2. * Binney (1), in, t. 13, f. e. 



