OF THE FOSSIL PLANTS OF THE COAL-MEASTJEES. 
697 
sions as seen in fig. 46. One of the lateral bundles ( m ") continues its outward course 
in the more horizontal direction which the upper portion of the similar bundle is seen to 
follow in fig. 43, producing the more elliptical form seen both in the section of the bundle 
itself and of the areole representing the missing cellular tissue by which the bundle 
was immediately invested. The second bundle ( m ') is now much smaller in size, and 
has not advanced so far as its companion from the point at which it entered the middle 
bark. I presume it is either going to some secondary rachis of smaller dimensions than 
that to which the larger bundle m" is proceeding, to become a secondary bundle in the 
same rachis as the larger one, or to become wholly abortive. It is not easy to deter- 
mine which of these suggestions is the correct one. We are here brought face to face 
with the same difficulty as that encountered in Bachiopteris duplex. For double 
bundles to enter a common rachis is an ordinary occurrence amongst recent ferns ; hut 
unfortunately I fail to discover amongst these fossil secondary petioles any so furnished. 
Their bundles appear to be single ones in all the plants of the Zygopteris type. 
Amongst many other specimens from the neighbourhood of Oldham, for which I have 
been indebted to Mr. J. Butterworth *, were the two represented in figures 49 & 50, and 
which are obviously the same plant as that described by M. Renault under the name of 
Zygopteris bibractiensis. The central vascular bundle has been somewhat disturbed, pro- 
bably by the shrinking of the inner cortical layer (g), rather than by any external pressure ; 
but it is easy to see that at a' we have the usual horizontal vascular bar, at the extremities 
of which we have the two vertical arcs (a, a), one arm of one of the latter being acciden- 
tally detached from its normal position at aa. Two features distinguish this vascular axis 
from that of the Z. Lacattii of Renault : — (1) all the vessels composing it are barred, 
none of them being reticulated ; (2) each of the two vertical arcs (a) consists of a 
double layer of vessels, very differently arranged from those of Z. Lacattii. As in the 
latter case this double layer consists of an inner series (a), the vessels of which are 
large, and an outer one (a") composed of much smaller vessels ; but in Z. bibractiensis 
these do not merely constitute a double series of larger and smaller vessels in such close 
apposition as to constitute but two portions of a common cluster, but the two sets of 
vessels are so arranged as to form one unbroken linear series, constituting a loop or 
circle, the two sides of which have been brought into close approximation. The very 
small area which this loop encloses has been shown by M. Renault to be occupied by 
a delicate parenchyma. The following is the terse description of this arrangement 
given by the French botanist : — “ Les bandes paralleles situees aux extremites de la ligne 
* Hr. Butterworth has recently furnished rue with a second and very beautiful example of this petiole. It 
agrees in every respect with the above description, except that in it the innermost cells of the inner hark, i. e. 
those in immediate contact with the large vascular axis, are very much smaller even than those forming the 
rest of that inner tissue. They almost form a special sheath to the vascular axis. This new specimen 
agrees with that described above in showing that the lacunae in the inner bark of the latter are the acci- 
dental results of desiccation. It differs, however, in not exhibiting any traces of the peripheral hairs (fig. 49, 1c). 
The hand of small vessels (fig. 49, a") is continuous and unbroken, as well as in close contact with each vertical 
bar (fig. 49, a) of the transverse section of the vascular axis. I still find no gum-canals in its hark. — Nov. 9th, 1874. 
