302 
R. H. Compton. 
the elongation becomes more and more marked and constrictions 
appear in both outer and inner tracts of tissue. A strand separates 
first from the internal parts of the compound stele and lies free 
in the ground-tissue as an ordinary haplostelic strand. The con¬ 
striction in the outer zone becomes more marked, and eventually 
Fig. 38. Diagrams of a series of transverse sections through the bifurcation 
of the rhizome. Xylem shaded with lines. Endodermis a dotted line. 
complete separation into two roughly equal portions takes place ; the 
result being in the one branch a typical dicyclic structure; in the 
other a similar structure but with the two cylinders still united, 
later, however, becoming separate. 
No ramular gap is produced in the process of branching. 
Frond. 
A transverse section of the petiole (Fig. 39) near its base shews 
a marked resemblance to that of the § Mertensia of Gleichenia 
(Poirault, 8, p. 176). The xylem consists of four groups of large 
tracheids united by bridges of smaller elements, the whole being 
arranged in the form of a distorted horse-shoe with incurved ends. 
The lumina of the large tracheids are often closed by accretions of 
a dark brown substance. 
There are three protoxylem groups consisting of narrow 
scalariform elements, these being situated in the regions between 
the groups of large tracheids. 
The centre of the petiolar bundle is occupied by a small strand 
of strongly thickened cells, of the same character as those of the 
cortical region. This is surrounded by an endodermis which is 
separate from the general endodermis of the bundle in this region. 
The internal and external pericycles are continuous with one 
another around the margins of the horse-shoe. The remainder of 
