240 Boodle and Worsdell. — On the 
The cortical bundles run down from the leaf through one 
internode along the edge of the palisade-tissue, and at the 
next node they pass in and unite with the central cylinder h 
Their xylem seems to consist of spiral elements only, which 
are very narrow. The elements of the phloem are so narrow 
that it is difficult to distinguish between the separate elements 
of which it is composed. 
An examination of the apex of the stem distinctly showed 
three merismatic layers extending round this region. But 
the initial cell or cells of each layer were not clearly dis- 
tinguishable from the adjacent cells. 
Anatomy of Older Stem. 
The transverse section of an older stem shows the forma- 
tion of periderm in a hypodermal position, beginning in the 
form of an arc round the base of the depressions, the ridges 
containing the palisade-cells still remaining in free connexion 
with the stem. At a little later stage the cork completely 
cuts off the ridges, whose cells now appear shrunk and 
shrivelled, and their contents brown and dead. Lecomte 2 
says that in Casuarina the periderm in the lower part of the 
ridge is formed outside the cortical bundle ; higher up it is 
seen dividing this bundle into two parts ; still higher up 
it appears on the inner side of the bundle ; the periderm- 
strand continuing thus its perpendicular course while the 
bundle passes obliquely outward. In the same transverse 
section the periderm may be seen in three different positions : 
either on the outside of a cortical bundle, passing through its 
centre, or again, on the inside. At some point in the inter- 
node the cortical bundle cuts through the periderm (as 
mentioned by Lecomte). This author, as we have already 
said, describes the assimilating ridges of the stem as leaves, 
and he compares their separation from the stem by periderm 
De Bary, Vergleich. Anat. cl. Phan, und Fame, p. 267. 
Loc. cit., p. 316. 
