Boodle . — Anatomy of the Schizaeaceae. 375 
tubes corresponding to those of other Ferns, but probably 
mixed with elements intermediate between sieve-tubes and 
phloem-parenchyma, and possibly somewhat reduced. 
The xylem is separated from the phloem by the usual ring 
of conjunctive parenchyma, and forms a complete round 
or oval zone, which is interrupted by the departure of the 
leaf-trace. The xylem-ring in vS. digitata is like that of 
the species figured (Fig. 11), but consists of a thinner layer 
of tracheides, which is usually 1-3 elements thick. The 
tracheides are scalariform with narrow pits, and are usually 
rather short, and often irregular. As in Lygodium , there are 
no definite protoxylem-groups, but the first formed tracheides 
are scattered. With such a thin ring of xylem it is difficult 
to determine whether the xylem is endarch or exarch, but 
Fig. 12, which represents the young node, shows that the 
development is irregular ; a. and b. are examples of an outer 
and an inner tracheide respectively being the first to differ- 
entiate. Protoxylem-formation in this case progresses from 
one side of the stem to the other. 
Within the xylem-ring is the pith, the cells of which are 
sclerotic, contain mucilage, and have numerous fine pits in 
their walls. The walls of the pith-cells adjoining the xylem 
are usually thinner than the rest, and* remain unlignified 
longer, and in these cells mucilaginous contents are less or 
absent. There is no internal endodermis. In the region 
of the leaf-gap the pith becomes continuous with the peri- 
cycle, and its cells, especially the outer ones, resemble those 
of the pericycle, which become fairly thick-walled and 
occasionally show pitting like that in the pith. The inner 
cortical cells also possess pits just like those of the pith-cells, 
but their walls are brown. The pith-cells are not very much 
elongated, being shaped like rather long parenchymatous 
cells and having often flat ends. 
There is a tendency to lignification in the pericycle and 
phloem. It was found by treating a section with phloro- 
glucin and hydrochloric acid that the tracheides were very 
strongly lignified. The pith-cells were fairly strongly lignified, 
