214 
PROFESSOR W. C. WILLIAMSON ON THE ORGANIZATION 
appearance of terminating at that line, which certainly is not the case*. The arrange- 
ment of the parenchymatous and prosenchymatous tissues in this section again corre- 
sponds very closely with that seen in the similar one of Favularia (fig. 32). But the 
most instructive part of the specimen is exhibited by the vascular bundle (fig. 42, m), 
consisting of several very minute barred vessels, and obviously surrounded by a thick 
mass of very delicate cellular tissue, which is parenchymatous, but with a tendency on 
the part of the cells to become elongated in the direction taken by the vascular bundle. 
Near the outer surface of the epiderm these cells become merged with the ordinary 
epidermal parenchyma. Where this cellular mass, in passing through the epiderm, comes 
in contact with the prosenchyma of the latter (fig. 42, i ), the tubes of the prosenchyma 
all bend inwards in the line of the vascular bundle : this is the case in each instance 
where my sections cross a leaf-scar. It will also be seen from fig. 42, that, at these 
points, the prosenchymatous tissue projects (/') into the subjacent bark. 
The entire thickness of this double layer has been fully a quarter of an inch. In the 
interior of the stone that of the opposite side is also preserved ; but every portion 
of the intervening bark, as well as of the central vascular cylinder and medullary axis, 
has disappeared. The specimen is in the condition in which all the flattened stems 
of the Sigillarire so common in the coal-shales doubtless have been, viz. a mere cylinder 
of epiderm, rendered tough and resisting decay through its inner layer of elongated 
fibrous prosenchyma, and having its two opposite inner surfaces brought into near proxi- 
mity as soon as sufficient pressure was applied to the sides of the stem. 
It is a remarkable circumstance that after the publication of the valuable and clearly 
illustrated observations on the structure of Stigmaria made by M. Brogxiart j% there 
should have been, in later years, so much misapprehension respecting this well-known 
plant. 
The first movement in the wrong direction originated with Professor Goeppert, who 
described a Stigmaria (‘ Genres des Plantes Fossiles,’ tab. 13) with vascular bundles pass- 
ing longitudinally through the pith, and from which he believed the vascular bundles 
going to the rootlets were supplied. In this he was followed by Dr. Hooker (Memoirs 
of the Geological Survey of ‘ Great Britain),’ who clearly affirmed the existence of medul- 
lary rays and bundles, but adopted Goeppert’s idea as to their origin. At this stage of 
the inquiry a very fine pyritized specimen came into my possession, a figure of which was 
given by Mr. Binney in the ‘Quarterly Journal of the Geological Society of London’ 
(vol. xv. pi. iv. fig. 1, a). This specimen, and others subsequently found by Mr. Binney, 
made it clear that the woody axis had been surrounded by a thick, but as yet unknown 
* The mistake is mine. I have more recently obtained evidence that, even in my specimens, these long, 
parallel-sided cells are bounded at their extremities by the horizontal lines, lc , as described by the French 
botanist. — May 5, 1872. 
t “ Observations sur la structure interne du Sigillaria elegans compare'e a celle des Lepidodendron et des 
Stigmaria et a celle des vegetaux vivants. Par M. Adolphe Prongxiart,” Extrait des Archives du Museum 
d’Histoire Naturelle, tab. 5. figs. 6, 7, & 8. 
