236 
PROFESSOR W. C. WILLIAMSON ON THE ORGANIZATION 
penetrating tlie bark, had emerged from the ligneous zone. He expresses himself very 
doubtfully as to the source of these bundles ; hut observing what he deems to be indica- 
tions of them in the transverse section of the outer ligneous cylinder, close to the inner 
one, he thinks they may possibly have originated in the latter. 
The third writer whose observations bear upon the question is Professor King, whose 
able and lucid paper* contains an admirable account of all that was known of these 
plants at the time when his memoir w 7 as published. In it he discusses the structure of 
the Anabatlira of Witham, having had in his possession a number of that distinguished 
observer’s original specimens. In this plant, as I have already mentioned in the pre- 
ceding memoir, we have the inner medullary cylinder and the outer ligneous zone of 
vessels arranged as in Brongniart’s Sigillaria and in Dijploxylon ; only, as in the latter 
plant, it constituted a continuous instead of an interrupted ring. Professor King calls 
attention to the large lenticular openings, seen in the tangential sections of the woody 
zone of Anabatlira , figured and described by Witham as medullary rays. He says 
respecting them, “Mr. Witham described these openings as containing the medullary 
rays, which is not the case, because what has probably been mistaken for cellular tissue 
is, in reality, a bundle of small vessels, similar to those which occupy the outer part of 
the medullary sheath. Although the longitudinal sections do not exhibit any of these 
bundles springing from the vascular cylinder, their proximity in some transverse sections, 
together with the fact just stated, leave no room to doubt their having constituted the 
leaf-cords of the plant.” This writer further adds, “ from these passages being in part 
vacant, it may reasonably be supposed that the cords were accompanied in their course 
with a portion of cellular tissue ”f. 
It thus appears that all three of the above writers inclined to the idea that the foliar 
vascular bundles arise from the vessels of the vascular medullary sheaths of the plants 
which they severally describe. In the previous pages I pointed out that whilst in some 
Hiploxylons the line of demarcation between the medullary sheath and the ligneous 
zone was a crenulatecl one, in others it appeared to be straight. Having recently pre- 
pared and examined a large number of additional sections, I find that even in some of 
the examples in which I thought the line was a straight one I can detect a series of 
small crenulations. This I have especially found to be the case with the specimen 
represented in figs. 20-23. In this plant the crenulations resemble those seen in fig. 34, 
though much more minute. The latter figure shows at d what appear to be angular 
projections of the medullary sheath penetrating between the large convex, inner extre- 
mities of the fasciculi of the woody zone. I now find that in the plant in question these 
projecting angles are not wholly occupied by medullary vessels , but contain a remarkable 
arrangement of barred cells. Fig. 23 a represents a small portion of a radial longi- 
tudinal section of this part of the plant, in which c represents the outermost vessels of 
the medullary sheath, e the inner vessels of the woody zone, and the cells b the structure 
* “ Contributions towards establishing the generic characters of the fossil plants of the genus Sigillaria, 
by William Ring, Esq.,” Edinburgh New Philosophical Journal, Nos. 71 et seq. 
f Loc. cit. p. 124. 
