OF THE FOSSIL PLANTS OF THE COAL-MEASURES. 
91 
h, h', and h" represent various sections of numerous peculiar peripheral appendages. 
Though so conspicuous when present, examples of this cortex are common in which 
no traces of these organs can be found. When perfect, each one is bottle-shaped, 
having a length of '05 of an inch and a maximum diameter of ’02. The superficial 
layer of each of these appendages is prosenchymatous, the cells being especially elongated 
and narrow near and at the terminal neck of the bottle. Internally the appendage 
consists of a very regular parenchyma, as is shown by the longitudinal and transverse 
sections h", h". Owing to the slight obliquity of the entire section fig. G, at h' li only 
the isolated projecting tips of these organs are seen. Many of my transverse sections 
of the Lyginodendron exhibit similar appendages ; thus, they are seen in fig. 1, h, and 
the basal portion of one is intersected at fig. 3, h. This latter, like many other similar 
ones, illustrates the nature of these structures. They are emergences, not hairs. 
Their internal parenchyma, li, is seen in fig. 3, to be an extension of the subjacent 
parenchyma, f', of the outer cortex, whilst the prosenchymatous superficial coat is 
derived from the two fibrous bands, g', g, by which f is hounded laterally. This 
explanation is yet better demonstrated by fig. 9, in which the two portions, h, li, of 
the emergence are seen to be respectively developed from the fibrous laminae, g, g, 
and from the intermediate parenchyma, f, of the outer cortex. 
The very characteristic emergences, h, of figs. 1-3 and 6, reappear in the petioles 
hitherto described under the name of Rachiopteris aspera. In my Memoir VI., I 
pointed oub^ the existence, on the periphery of these petioles, of numerous “ abortive 
hairs” or “tubercles,” but I was not then aware of their full significance. 
Fig. 7 represents a characteristic example of a transverse section of a young 
Rachiopteris aspera, from the periphery of which a number of these emergences, A, h, 
are given off. The origin of the superficial layer and of the internal parenchyma of 
each emergence' is seen to be identical with that demonstrated in my description of 
fig. 9. Fig. 8 represents a longitudinal section of a similar petiole, in which these 
emergences are again seen at A, A, variously intersected. 
The above facts combined make it clear that Rachiopteris aspera is merely a petiole 
of Lyginodendron Oldhamiiim ; hence the former name must disappear from our lists. 
It also follows that Lyginodendron Oldli,amiitm is a true Fern, most probably belonging 
to some Sphenopterid type. This determination carries along with it the further one 
that the stems of some, at least, of the Ferns of the Carboniferous age developed their 
xylem or vascular structures exogenously, through the instrumentality of a meri- 
stemic zone of the innermost cortex, which practically must he regarded as a cambium 
layer. But the history of this interesting plant is not yet ended. 
In various preceding memoirs, but notably in Part XVI., I have provoked a strong 
opposition amongst some botanists whose studies have been chiefly limited to living 
forms of vegetation, by revealing the existence, amongst the Lycopodiaceous plants of 
the Coal Measures, of a mode of development of a medulla which differs so widely from 
* Plate 52, figs. 8, 9, aud 1.3, tc, k", pp. 681-2. 
