OF THE FOSSIL PLANTS OF THE COAL-MEASUKES. 
217 
cylinder at d. In fig. 4, d, we discover this same bundle completely detached from the 
central axis and proceeding direct to the periphery of the cortex. In the longitudinal 
section, fig. 21, we have, at d, a corresponding bundle. In both these examples these 
secondary bundles obviously ascend through the stem as they proceed outwards, in exactly 
the same way as the larger primary petiolar ones do. Though following the same 
course, the former are very much smaller, both in their aggregate diameter and in the 
size of their component vessels, than the latter are. The entire series of sections appears 
to exhibit them of two sizes. In figs. 4, d, 7, d, & 8, <7, each bundle has a diameter of 
•032, whilst in figs. 5, d, 10, d, & 12, d, it is only -01 in thickness. It is another notable 
point in these eleven consecutive sections, that whilst we only find two of the large 
primary bundles (d) emanating directly from the central cylinder, we have certainly five 
of these smaller ones doing so. In fig. 7, as shown in the enlarged representation, 
fig. 20, d, the secondary bundle is seen springing almost from the central axis simul- 
taneously with the primary one V . 
But we further find secondary bundles arising from the primary petiolar ones. We 
have one such originating at cU from the primary bundle, fig. 5, c'. In fig. 6, d', we find that 
this secondary bundle has reached the periphery of the stem, and, as seen in fig. 24, d', 
which represents this bundle and its surroundings enlarged 18|- diameters, it is now the 
centre of a distinct organ somewhat similar to fig. 18, but having little more than one 
third the mean diameter of the latter section. Traces of this appendage are still seen in 
figs. 7, d' & 8, d', but in fig. 9 it has wholly disappeared. The correctness of this description 
depends upon the identification of the bundle, fig. 6, d with fig. 5, d'. But on recurring to 
figs. 2, 3, & 4 we find a curious bundle unaccounted for at d in each of these sections. 
It must be remembered that fig. 2 is the lowest of this series of sections, and that as we 
ascend in the series we ascend in the stem. Observing that the small bundle, fig. 2, is 
further removed from the primary bundles c than in the sections figs. 3 & 4, it appears 
possible that these latter bundles may be identical with d in fig. 5. If this be the case, 
we have here an instance in which a secondary bundle descends as it passes outwards 
through the bark, instead of ascending, as we have seen to be the case with the small 
bundles given off from the central cylinder. Such an arrangement would correspond 
exactly with that so common amongst such living ferns as Aspidium Filix Mas , where 
the bundles of vessels supplying the adventitious roots spring from the petiolar bundles, 
subsequent to the separation of the latter from the true axial bundles of the stem. 
The discovery of fresh specimens can alone settle this point. 
Two questions still remain to be answered, viz., what is this stem'? and what is the 
morphological significance of its various parts ? 
As I have already observed, M. Renault has described two stems which have the 
axial vessels arranged as in the subject of the above description, an arrangement which 
differs very widely from what is seen in any known ferns, recent or fossil. The detached 
bundles of fibro-vascular tissue seen in recent ferns, whether of the herbaceous or of 
the arborescent type, exhibit no arrangement exactly corresponding to the closed 
