OF THE FOSSIL PLANTS OF THE COAL-MEASUKES. 
309 
in the preceding pages. At its upper portion we have on the left hand the leading shoot, 
and on the right the lateral branch of a Lepidodendron , with their leaves in situ and the 
central vascular axis of each limited to a medullary cylinder (c) enclosing a true pith («). 
Lower down we have the later-fonned layers of the exogenous zone (d). The leaves 
are here represented by their petiolar bases (/'), whilst yet lower we find that these have 
disappeared, leaving only the ordinary Lepiclodendroid scars ( y ). Below the level of the 
black ground-line we have the Stigmarian roots, Avith their rootlets (o) and their rootlet- 
bundles of vessels (oi), derived from the exogenous zone (d 1 ). 
In my last memoir I described a very peculiar variety of bark which I frequently found 
associated with the Lancashire forms of Diploxylon. Nothing resembling it occurs in 
the bark of the Burntisland type. In one of the Lancashire types, as I have already 
stated, I found the cells of the medullary rays thickened by internal bands of lignine, 
rendering them scalariform. No such cells appear in the Scottish plant. These are 
probably specific distinctions, to learn the exact value of which will require prolonged 
research. 
I have now brought together the representatives of four distinct genera. The young 
twigs which I have described, whether we are guided by their outward forms or their 
internal structure, are true Lepidodendra. The older and larger branches and stems 
have the internal organization of a Diploxylon Avith the external bark and persistent 
petioles of a Lomatophloios, Avhilst the branching stems, Avith their double ligneous 
axes, are unmistakably identical with the Leptoxylon of Coeda *. The broad features 
of resemblance in the cortical and petiolar portions of my plant to Coeda’s minutely 
described Lomatophloios crassicaule are too manifest to require that I should dAvell upon 
them. The disciform Sternbergian pith of Corda’s species does not recur in any of our 
British forms. All such modifications of pith that have come under my notice continue 
to be correctly located where I placed them many years ago, viz. in the woody cylinders 
of Dadoxylons. But the possession of a disciform pith is not recognized as constituting 
a generic distinction amongst recent plants, and Ave need not give it that value amongst 
fossil ones. Corda’s genus Leptoxylon was founded upon a single decorticated axis, 
which, so far as it remains, displays no single feature differing from those of Diploxylon, 
except in the double character of the axis. Brongniart has already shown that this 
feature Avas but a result of the branching of the stem, and I have further illustrated the 
same truth in the preceding pages. Of the above names, the most appropriate one to 
be retained would be that of Lomatophloios , were it not clear that this is also a synonym 
of Sternberg’s older term Lepidopthloiosf: Brongniart has already adopted the latter 
name, uniting Avith it Corda’s genera Lomatophloios , Leptoxylon , and Calamoxylon, 
Sternberg’s Cycadites columnar is, and Goeppert’s Pachyphyllum% , all of which generic 
terms except Cycadites he abandons. It is obvious that Anabathra and Diploxylon must 
* Flora der Yorwelt, tab. 15, p. 21. 
t Dr. Daavsox further considers Ulodendron to be merely a synonym of Lepidophloios. 
t Tableau des genres de Vegetaux Fossiles, pp. 43, 44. 
2 t 2 
