90 
PROFESSOR W. C. WILLIAMSOR’ OR THE ORGANISATION 
of this plant; e, the outermost cortex, composed, in transverse sections, of radiating 
bands of sclerenchyma, fj, alternating with parenchymatous areas, f. At Jz, Jc vze find 
two bundles of tracheids, like those at d, forming the centre of the cortical structures 
of a petiole of Rachioj^teris aspera, i, i, which petiole is organically united to the 
cortex e of tire Lyginodendron. The two bundles Jz are assuming the oblique 
relative positions seen in the similar bundles of the free petiole of R. aspera, repre¬ 
sented in fig. 2. (3ther sections in my cabinet, similar to fig. 1, demonstrate the 
same facts, viz., that the pairs of bundles, fig. I, d, whiclr form so characteristic a 
feature of transverse sections of the middle cortex of Lyginodendron Oldhamium, pass 
outwards, through the outer cortex, to become the tracheseal" bundles of the petioles 
of the plant, and wliich petioles I had previously designated Raehiopferis aspera. I may 
state that my friend Graf Solms-Laubach, who has obtained numerous specimens 
of the Lyginodendron associated with others of Rachiopteris aspera from a locality 
on the continent, agrees with me in the conclusion at which I have arrived respecting 
their unity. The more perfect specimens of the Lyginodendron obtained during the 
last seventeen years have thrown yet further light upon those figured in 1873. In 
the latter, as at fig. 1, c, no traces of the middle bark were preserved ; but examples 
from Halifax, for which I am indebted to my friends Mr. Cash and Mr. Spencer, of 
Halifax, have supplied what was wanting. Fig. 3 is a transverse section in which 
this inner cortex, c, is shoAvn to consist of a zone of extremely delicate, thin-walled 
parenchymatous cells, scattered throughout which are numerous gum-canals, 1. Three 
of these canals are represented, enlarged 250 diameters, in figs. 4 and 5, embedded in 
the thin-walled cells, c, c, of the cortex. 
These canals are obviously formed by a schizogenetic separation of the cortical cells, 
c, and display no signs of having possessed the linings of epithelial cells so frequently 
seen in the similar canals of living plants. Each canal is lined by a thin carbonaceous 
layer, a, within which is a free carbonaceous rod, h, with a round or oval section. I 
presume that both these black elements are the carbonised remains of gums or resins 
with which the canals were j^rimarily filled. 
Fig. 3, h' I)', show^s an unusual occurrence of laminse of tracheids growing inwardly 
into the medulla, to be referred to later. 
Another feature characterising equally the outer cortex of Lyginodendron and that 
of its petioles is well shown in fig. 6, which represents a superficial tangential section 
of the cortex of Ijyginodendron Oldhamium. At its lower part this section repre¬ 
sents the structure already described in Memoir IV. The fibrous bands g and the 
cellular areas f correspond to those indicated by the same letters in figs. 1 and 8, but 
* I have, throughout this Memoir, used the term trachea} in the sense in which it is iised by de Bary 
as comprehending both the shorter, thickened, but elongated cells, tracheids, and the longer trachece or 
vessels. De Bary" does so “ specially in those cases where it is not certainly decided whether a tube 
belongs to the one or to the other subdivision,” which is almost always the case amongst these coal 
plants. (See de Bary ‘ Comparative Anatomy of Phanerogams and Ferns,’ p. 155.) 
