932 PROFESSOR W. C. WILLIAMSON AND DR. D. H. SCOTT ON THE 
outer limit of the wood is sharply defined ; next comes a layer of excessively delicate, 
elongated cells, doubtless the cambium. Further to the exterior we find a zone of 
long, thin-walled elements, some of which are of considerable diameter, and are some- 
what dilated at the transverse septa. These evidently correspond to the large, thin- 
walled cells of the transverse section. The resemblance of these elements to the 
sieve-tubes of the higher plants is very striking, nor are sieve-tubes of similar form 
unknown among the vascular Cryptogams. In Marattia, for example, they are some- 
times quite of this type. We think it quite possible that these elements in Spheno- 
phyllum insigne may really have been of the nature of sieve-tubes. 
Still further towards the outside we find the very regular, short-celled periderm ; 
its inner cells have thin walls, and no doubt represent the phellogen. The gap in the 
figure, separating the periderm from the phloém, is merely a local lesion, for, in other 
parts of the same section, all the tissues are continuous. 
From the study of the transverse section, as a whole, it appears that the phloém 
was not equally developed all round the stem, but was specially localized at certain 
points. 
The periderm attained a great thickness; in the largest specimen four distinct 
zones can be recognized, so that here, as in S. plurifoliatum, there was evidently a 
repeated formation of phellogen in successively deeper-seated layers. This great 
development of internal periderm, and consequent throwing-off of the whole primary 
cortex, seems to have been a striking characteristic of the genus. 
Before concluding our account of this species we will return to a specimen, already 
referred to, which shows the base of a lateral appendage. The section in question* is 
an incomplete transverse one, showing only one angle of the primary wood. About 
ten layers of secondary wood are present, and both primary and secondary cortex are 
fairly preserved. Opposite the protoxylem-group a large bundle of scalariform or 
reticulated trachez, accompanied by parenchyma, runs out in an horizontal direction. 
The outgoing strand is too large for a leaf-trace; it must have belonged either to a 
branch or an adventitious root. The cortex appears to be ruptured at the exit of the 
strand. On the whole, we are inclined to regard the appendage as a root, for its 
origin seems to have been endogenous. No certain conclusions, however, can be 
drawn from this isolated specimen. 
To sum up, we find that the chief anatomical characteristics of Sphenophyllum 
insigne, are the following : 
1, The presence of a canal at each angle of the primary triarch xylem. 
2. The scalariform thickening of the secondary trachez, at least as regards their 
radial walls. 
3. The presence, throughout the secondary wood, of continuous medullary rays. 
* C.N. 926 (see Wittiamson, loc. cit., Part V., Plate 5, fig. 27). 
