412 Boodle . — Anatomy of the Schizaeaceae. 
elements in the region corresponding with the concavity of 
the xylem-arch in Anemia , and a suppression of the xylem 
external to the three protoxylem-groups, except in the case 
of the median group in L. palmatum, together with a splitting 
of the median group except in L . palmatum. In both Anemia 
and Lygodium the median group (or pair of groups) differenti- 
ates before the others. In Schizaea only the median endarch 
group appears to be present. Possibly one median endarch 
protoxylem-group is primitive for the Order, and the lateral 
groups have been added in connexion with increase in size of 
the bundle. The protoxylem-groups in the petioles of all the 
genera contain spiral or annular elements, but in Lygodium 
and Schizaea spiral elements are absent in the basal region 
of the petiole ; but in Lygodium at any rate small early-formed 
scalariform tracheides occur in a nearly identical position to 
that occupied by the spiral elements higher up. The term 
‘ protoxylem ’ appears applicable to these. In the Schizaeaceae 
the stem-protoxylem does not occur in definite groups, but 
is represented by scattered tracheides which are scalariform. 
No spiral tracheides are present in the stem except in Anemia 
and Mohria , where a spiral protoxylem of the leaf-trace is 
continued a short distance down in the stem. Gwynne- 
Vaughan (’01, p. 87) has laid stress on the distinction between 
stem- and leaf-protoxylem in Loxsoma\ and it certainly 
appears probable that the differentiation of stem-protoxylems 
in close relation to leaf-trace-protoxylems may be a com- 
paratively late character. Where the xylem is of considerable 
thickness the protoxylem-elements of the stem are at or near 
the periphery. 
Sclerosed sieve-tubes, forming fibres in the petiolar bundle, 
occur in certain species of Lygodium , Schizaea , and Anemia , 
but not in Mohria. 
Fibres of this kind are uncommon among Ferns. Their 
presence here, and the occurrence of 1-2-celled glandular 
hairs on the stem and petiole, and of silica-deposits, within 
the cell-cavity (in Lygodium :), or in the form of knobs in the 
outer walls of epidermal cells (in Schizaea and Anemia) may 
