OF THE FOSSIL PLANTS OF THE COAL-MEASURES. 
199 
rays. At e we liave the itinermost zone of the cortex, as at fig. 115, e. The external 
cortex consists of a coarser parenchyma. 
The next example to be described has a marked individuality. I propose giving to 
it the name of Lepidodendwn Spenceri, after my friend Mr. J. Spencer, of Halifax, 
who has so long been one of the most active of my several auxiliary collectors, to 
whom I have been so much indebted. 
Fig. 19 is a transverse section of a stem or branch of this plant. The central 
structure, a, exhibits in this section no indication of medullaiy cells, but appears to 
be a solid rod of scalariform tracheids. It is surrounded at e by a narrow zone of the 
inner cortical parenchyma, the greater part of which has disappeared. At f is the 
middle cortex, characterised by an undulating outline, the outward prominences of 
which are frequently prolonged into points, y'. Fig. 20 represents one of these points 
further enlarged. In it, at e, we again have the zone of the inner cortex ; at_/ is the 
middle cortex, and at/' we find the barred vessels of a foliar bundle passing outwards. 
The cells of which the middle cortex, / is composed are not uniform in structure ; 
dark, dense masses of thick-walled cells (fig. 19,/") alternate with lighter groups with 
thinner cell-walls,/"', In the centre of most of the darker groups of several of my 
specimens the tissue has become decayed, as at fig. 19,/". This variation in the 
structure of the middle cortex appears to be a very characteristic feature of the 
species. None of my sections retain any traces of the outermost cortex and its foliar 
organs, 
In hg. 21 we have a radial section of the above cortical zones; at a are two or 
three of the outermost vessels of the central bundle, giving off at a' a foliar bundle 
passing upwards and outwards through the middle cortex. This cortex chiefly 
consists of strongly-defined prosenchymatous cells. In fig. 22 we have a vertical 
section through the centre of the vascular axis, a, of fig. 19. We see some prosen¬ 
chymatous but thin-walled cells belonging to the inner coi tex at e, through which a 
foliar vascular bundle is again escaping at a. 
On turning to the section through the vascular axial tissue (fig. 22), we find some 
interesting features. 'Its exterior, a, a, consists of developed and strongly-defined 
barred traclieids; but the centre of this structure, a", consists of thin-walled, 
unbarred, and much-elongated fusiform cells, whilst we have some very thin-walled, 
barred tracheids, but in which the bars are so thin as to be almost invisible. It is 
obvious that we have here a procambial string which is undergoing centripetal 
development into a vascular bundle, the more external tracheids, a, of which have 
undergone perfect lignification. Those indicated in fig. 22 by a", a" are but partially 
lignified, whilst in the central part, a”, we have procambial elements which the 
process of lignification has not yet reached. This is the only specimen in which I have 
personally seen a Carboniferous example of a centripetally-developed vascular bundle. 
What appears to have been a somewhat similar one is referred to by M. Renault as 
occurring in his Lepidodendron RliodumnenseT' 
'* ‘ Coin’s de Botaniqne Fossile,’ D'enxieme anree, p. 23. 
