STRUCTURE AND AFFINITIES OF A LEPIDODENDROID STEM. 925 



the distinguishing features between the two species. There are other differences which 

 need not be considered here, as they are well known and apparently constant. The 

 " bast-fibres " of the leaf-trace are referred to by Bertrand # as consisting in part of 

 possibly laticiferous tubes, and that they are not bast fibres but brown secretory cells 

 is, we believe, the true explanation. Precisely similar groups of indistinctly preserved 

 cells accompany the leaf-traces of L. fuliginosum, and these two are composed of a few 

 partially-disorganised secretory elements. A comparative examination of the species 

 Lepidophloios Harcourtii, L. fuliginosus, and L. Wilnschianus shows that in each of 

 these plants there is a fairly broad zone of secretory tissue a short distance beyond the 

 xylem, as shown in several of the photographs of the Dalmeny stem. As the xylem 

 tracheids of a leaf-trace pass into this zone they appear to carry in front of them a patch of 

 the secretory tissue. A leaf -trace bundle when seen immediately external to the primary 

 xylem of the stem has no strand of the so-called fibres accompanying it ; but imme- 

 diately beyond the secretory zone the second strand is present, and it consists, we 

 believe, not of true fibres, but of somewhat crushed or partially-disorganised secretory 

 cells, t This behaviour of the trace is very clearly demonstrated in some sections of 

 L. fuliginosus, figured by Binney j under the name of L. Harcourtii, and now in the 

 Woodwardian Museum, also in several sections of L. Wilnschianus § and L. Har- 

 courtii in the British Museum. A more detailed account will be given of the Binney 

 sections in another place. || 



Another point of resemblance between L. Harcourtii and the Dalmeny plant is the 

 occurrence of strands of secretory cells in the outer cortical region. In the type- 

 specimen of Witham's species there are a few large canals near the periphery 

 of the partially decorticated specimen ; and in the large stem from Airdrie IT we find 

 large canals just internal to the phelloderm precisely as in the Dalmeny stem, as well 

 as other canals in the phelloderm tissue. In the Dalmeny plant the secretory areas 

 immediately internal to the phelloderm (region b PL I. fig. 2) are rather larger than 

 those in the phelloderm ; in L. Harcourtii there is the same slight difference between 

 the more internal and external canals.** Bertrand tt has figured a secretory area in 

 the cortex of a specimen of L. Harcourtii received from M. Hovelacque. 



The short tracheids which occur in the inner margin of the primary wood of the 

 Dalmeny stem (PL IV. fig. 25) are clearly represented in L. Harcourtii.^. The margin 

 of the corona in L. Harcourtii and in the Dalmeny stem is, we believe, identical, and 

 the leaf-traces apparently become detached from the main mass of xylem in the same 

 manner (figs. 24 and 34). The mesarch structure of the leaf-traces is another character 

 shared by L. Harcourtii §§ and the Scotch plant ; the same feature is well shown in 



* Bertrand (91), p. 119. t Gf. specimen 448A, 456 A, etc. 



{ Binney (72), pis. xiii. and xv. Gf. also specimens 1922A, 384, etc., in the Williamson Collection. 

 § E.g., sections Nos. 465, 448 A, 428. 



|| [Since this was written a description of Binney's specimens has been published in the Proceedings of the 

 Cambridge Philosophical Society, vol. x. p. 137 ; vide Seward (99).] 



1 Figured by Williamson (93), pi. i. fig. 3. ** Gf. specimens Nos. 1593, 380, 381. 



tt Bertrand (91), pi. v. fig. 26. + + Specimen No. 381. §§ Ibid. (91). 



VOL. XXXIX. PART IV. (NO. 34). 7 C 



