372 Boodle . — Anatomy of the Schizaeaceae . 
and may be regarded as belonging to the stem. To take one 
case as an example for the details : — during the double 
bending of the stele, the xylem-tracheides become’ more 
nearly uniform in size, and increase in number from 15 to 
about 36, at the same time the outline of the xylem becomes 
roughly circular, definite protoxylem-groups are not dis- 
tinguishable, and the phloem becomes practically continuous. 
Then, to return to the general description, a few parenchyma- 
cells appear in the xylem, and a little higher up they increase 
in number, so that the structure of the rhizome of a mature 
plant is represented on a small scale, as seen in Fig. 9. 
This is from a section below the first leaf ; p. is one of the 
xylem-parenchyma-cells. In Fig. 10 the xylem of the first 
leaf-trace has just separated from the xylem of the stele. 
From two to three leaf-traces and from one to three roots 
are given off (in the order of first a leaf-trace and then a root), 
the stele meanwhile retaining the type of structure shown in 
Fig. 9. After this the stem dichotomizes and leaves and 
roots are produced by the two branches of the stem, which 
grow as rhizomes. One of them is usually horizontal, while 
the other is inclined upwards, and, as stated above, one of 
them tends to be arrested. At this first dichotomy the 
branch cut transversely near its base shows the same type 
of structure as the rhizome of the mature plant ; paren- 
chyma is scattered among the xylem, and the largest 
tracheides are towards the centre of the latter, while the 
protoxylem is peripheral or nearly so. To return to one 
of the series for the orientation : the first leaf-trace separates 
from the stele on the side away from the prothallus, about 
in the position of an original root-protoxylem. The second 
leaf passes off towards the prothallus at a divergence of about 
120 degrees. The stele of the stem elongates in a plane 
about perpendicular to one which includes the two leaves, 
and then dichotomizes. Each branch gives off a root on its 
lower side, and one branch close to its base produces a leaf- 
trace on its upper side. 
It is clear from the above description that the structure 
