Comparative Anatomy of the Casuarineae . 243 
a branch is passing in, there will appear a gap in the central 
cylinder comprising about one-third of the whole section. 
This gap is filled with loose, parenchymatous tissue, dotted 
with large numbers of scattered tracheides with a tolerably 
thick wall. At the sides of the gap many of the elements 
can be seen joining on to the central cylinder, but the majority 
of them consist of the protoxylem-elements of the branch 
which are passing obliquely inwards to the centre of the 
stem. They give a characteristic appearance to the section. 
For some distance below the point where the tracheides have 
all united with the central cylinder of the stem the large ray 
thus formed is still present. These tracheides were described 
by Goeppert 1 and Lecomte 2 . The former figured them 
roughly in a tangential section of C. torulosa , Ait., but did 
not account for their appearance. 
A longitudinal radial section of a woody stem of Casuarina 
shows the phloem to consist of sieve-tubes with very oblique 
terminal walls on which several sieve-plates are scattered. 
These sieve-tubes are very narrow and the companion-cells 
are not easy to distinguish (Figs. 13-15). 
Most of the medullary rays in the wood are several cells, 
some only one or two cells thick. The most common form of 
ray consists of square, very thick-walled cells, with simple pits 
in their lignified walls, and often copious contents of starch, 
&c. In one or two cases a bordered pit was noticed in a wall 
of one of these cells, which was void of contents, thus con- 
stituting it a tracheide. In some species there were two 
kinds of rays : those above described, and others with thinner- 
walled cells which are narrower and elongated radially. 
Parenchymatous tissue amongst the elements of the wood 
is abundant. The cells composing it are of various shapes 
and sizes ; they are sometimes short and narrow, at other 
times broader, or much more elongated. Their walls are 
often considerably thickened. They invariably have contents. 
The more elongated cells of this tissue, which undergo no 
1 Loc. cit. 
2 Loc. cit., p. 315. 
