376 Boodle. — Anatomy of the Schizaeaceae . 
except the outermost layer of the wall, which was not lig- 
nified ; but the peripheral cells of the pith had hardly more 
than the middle lamella lignified. In the pericyclic cells the 
wall at the corners was often lignified, sometimes the middle 
lamella as well, or sometimes the greater part of the wall. 
The sieve-tubes sometimes had their walls lignified at the 
corners. The lignin stain was not seen in the sclerotic cortex. 
The middle lamellas of the cortical cells, pith and peri- 
cycle were curiously resistent to sulphuric acid, and were not • 
dissolved by boiling for a short time in potash-solution. 
The stem-structure of 5 . dichotoma and 5 . fistulosa , Labill., 
was examined in fragments of dried material. The figure 
5 . dichotoma (Fig. n), and the diagram of the same species 
(Fig. 1 5) will be referred to in the description of the node. 
The structure of 5 . dichotoma (Fig. 11) need not be described 
at length, as it is of the same type as .S', digitata , but it 
should be mentioned that one or two fibrous sieve-tubes, 
apparently lignified, occurred in the phloem near the two 
ends of the arc of xylem belonging to the stem. The smaller 
tracheides are usually at or towards the periphery of the 
xylem. Two or three layers of thin- walled cells with small 
intercellular spaces at the corners lie between the brown outer 
part of the cortex and the endodermis. 
In 5 . fistulosa there is a broad cortex consisting of fairly 
thin-walled cells, of which the outermost one or two layers 
only are coloured brown. The pith-cells are also fairly thin- 
walled, but have collenchyma-like thickenings at the corners. 
The xylem is only 1-2 tracheides thick, but where it is two- 
layered, if the tracheides differ in size, the smaller ones are 
nearly always at the outside ; so the structure tends to be 
exarch. Another piece of rhizome of this species was prob- 
ably a short distance behind a dichotomy, as it had two 
nearly equal-sized steles, both of which were slightly irregular, 
and the xylem was more or less interrupted by leaf-gaps. 
The two steles had been giving off leaf-traces ; three had 
been derived from each stele and were found at different 
distances on their way out through the cortex. 
