Boodle.— Anatomy of the Schizaeaceae . 383 
a layer of conjunctive parenchyma, but several fibres may 
also be in contact with the xylem. The pericycle forms 
a continuous layer of rather large cells, and is 2-4 cells 
thick, but reduced to a single row of cells on the flat top of 
the arch and at the ends of the arms. In these regions its 
cells have dense contents. The endodermis is very distinct, 
and roughly follows the outline of the xylem. Cavity- 
parenchyma 1 , which belongs to the conjunctive parenchyma 
adjoining the xylem, occurs in connexion with the three 
protoxylem-groups, but is most marked in the case of the 
median group, where two enlarged cells of this tissue may 
be recognized in Fig. 17. A cell belonging to the cavity- 
parenchyma is shown in longitudinal section in Fig. 18. It 
contains a nucleus and protoplasm, and has formed two large 
protrusions, which have grown into the space originally occupied 
by an annular tracheide of the protoxylem. Some of the rings 
of this element are seen crushed together at r. 
The epidermis and the succeeding five or six layers of the 
cortex are sclerotic, and there is a gradation from the small- 
celled epidermis to the large-celled inner layer of this zone. 
The rest of the cortex or ground-tissue is thin-walled. In 
cells of this tissue not far outside the endodermis a few silica- 
nodules were met with. They were usually solid-looking, and 
roundish or irregular in form. Fig. 20 is one of them, and is 
double, with a cavity in each half. 
In the basal region of the petiole the fibres become reduced 
in number until none are left. The top of the xylem-arch 
becomes more rounded, and the hooks become less incurved, 
until nearly absent. There are still three protoxylem-groups 
in the same positions as before, but, close to the base of the 
petiole, the median protoxylem appears to be the only one 
which possesses spiral tracheides, and is formed a little earlier 
than the other two. The ground tissue becomes fairly thick- 
walled, and the part of it filling up the concavity of the arched 
bundle becomes specially thick-walled. 
The leaf-trace in the cortex of the stem resembles the 
1 This tissue will be referred to again below. 
