502 
PROFESSOR W. C. WILLIAMSON ON THE ORGANIZATION 
the interior of several of these bracts I observe a slender vascular bundle composed of 
two or three minute barred vessels. 
Fig. 12 represents the cellulo-vascular axis of fig. 11 ; in its centre, a, is the 
cylindrical medulla, composed of parenchymatous cells. It has a maximum diameter 
of about *01. Surrounding this is a vascular zone, b, composed of barred vessels, not 
arranged in radiating lines, and remarkable for the approximate uniformity of their 
size. This cylinder, which has a mean diameter of about '034, exhibits several inden¬ 
tations, c, in its outer margin as if characterised by a tendency to break up into sepa¬ 
rate wedges. I am unable to say whether this is a normal feature or whether it is a 
result of partial dessication, but the same feature presents itself in both my sections. 
The individual vessels range from '0016 to '001 in diameter, the peripheral ones being 
the smallest. Surrounding this vascular axis is a sheath, cl, of very delicate paren¬ 
chymatous cells, radial prolongations of which, cl', cl', composed of similar but more 
elongated cells, proceed outwards. Though I have detected no vascular bundles on 
these cellular prolongations, I have no doubt that they accompanied such bundles in 
their passage outwards to reach the sporangiferous bracts. It will be observed that 
the specimens nowhere exhibit traces of the orientation of these bract-bundles, neither 
do we see any traces of transverse sections of them grouped around the vascular axis 
such as constitute so striking a feature of the corresponding sections of true Lepi- 
dostrobi. Otherwise the general features of these sections correspond with those 
previously figured in possessing a generally Lycopodiaceous aspect. A very large un¬ 
occupied space separates the inner bark (fig. 11, c) and the more robust outer cortical 
zone cl, which space was doubtless originally occupied by a delicate middle parenchyma¬ 
tous layer. The disappearance of this layer, leaving a thin inner zone like fig. 11 , d, 
surrounding the vascular axis, is a common feature of the Lepidodendroid axes both in 
stems and fruits. At the same time the structure of this newly-discovered vascular 
axis agrees with the features previously described in giving to this strobilus a very 
distinctive individuality. This strobilus may be named Lepidostrobus insignis. 
Fig. 12a represents a transverse section of an object from the Halifax deposit, 
for which I am indebted to Mr. Spencer ; its mean diameter is about '033. It is 
evidently a section of the upper extremity of either a fruit or a young shoot with 
pentamerous phyllomes alternating in contiguous verticils. The only plants with 
which we are at present acquainted having verticilate phyllomes are Calamites 
Sphenophyllum, Annularia, Asterophyllites, and their immediate allies ; but I have seen 
nothing amongst them that corresponds with this organism. The nearest approach to 
it is perhaps the little fruit figured in my last memoir (Plate 25, fig. 103), but even in 
this case the resemblance is but. remote. In the fruit Ccdamostacliys Binneyana the 
phyllomes are also arranged in alternating verticils ; but in them we find an liexa- 
merous arrangement, six fertile bracts alternating with twelve sterile ones. 
Since the publication of my fifth memoir I have obtained some additional illustra¬ 
tions of the structure of Calamostachys Binneyana. 
