Anatomy of the Cone and Fertile Stem of Equisetum . 241 
eccentric, and in the longitudinal reconstruction it has been shown on the 
strand on the radius of which it occurs considerably further in. The manner 
of its ending in a downward direction could not be ascertained, owing to 
the disturbance of the cells of the pith in which it was embedded ; but the 
strand was clearly a short one. Even where it is preserved, the incipient 
disintegration of the central tissue of the cone makes it difficult to ascertain 
the details of its structure. It seems to consist of numerous tracheides 
mixed with unlignified parenchyma, much as do the normal bundles, and 
of small cells pointing obliquely outwards, resembling those inside the peri- 
cycle of the normal stele, cells which we may provisionally term phloem. 
The orientation of this strand is therefore nearly normal. 
In Cone B such medullary tracheides as have been preserved are 
arranged very irregularly, many running for a part of their course hori¬ 
zontally or obliquely across the cone. The medullary strand consists 
of elements similar to those of Cone A, but the phloem-like cells are 
distributed irregularly on all sides, while irregular endodermal markings 
may be seen in some of the cells outside the tracheides. In a vertical 
direction the extent of this medullary strand is very small, and passing 
upwards it dies out as two very small groups of tracheides, separated 
by a few phloem-like cells. 
In the branched cone, C, these medullary strands are much more 
important. There are two of them, quite independent of one another. 
Throughout their course they remain at very much the same depth in the 
pith, but the larger one does not run quite vertically, being found now on 
the radius of one bundle, now on that of one of its neighbours. The 
lower and larger medullary strand originates about 1*5 cm. from the main 
apex of the cone ; it extends into four internodes, and its total length 
is nearly 5 mm. Its branchings, the variations in its width and its course 
with reference to the radii of the bundles, can be seen in the longitudinal 
reconstruction (Text-fig. 4, p. 250). As regards radial depth, this strand 
occupied a position rather more than half-way out between the centre of the 
pith and its periphery. If we trace its course from below upwards we find 
that before any tracheides appear there is a little patch of about eight thick- 
walled cells, noticeably smaller than those of the pith. These cells are 
from six to fifteen times smaller than those of the pith, the variation in size 
occurring not in the cells of the medullary patch but in those of the pith. 
Outside this patch of thicker-walled small cells the thin-walled cells 
increase gradually in size until we reach the large cells typical of the pith. 
Very soon, before any tracheides appear, small phloem-like cells are to be 
found facing obliquely outwards ; a little further up two or three tracheides 
identical with those of the normal bundle make their appearance. The 
tracheides and phloem-like cells increase in number, and the latter spread 
round the former until they nearly enclose them. These phloem-like cells 
R 
