426 Farmer and Freeman . — On the Structure and 
chium and especially in Ophioglossum , but they are perhaps 
rather less abundant in Helminthostachys than in the two 
other genera. 
As the leaves approach maturity they press on their cover- 
ing flaps, and finally rupture them ; hence when expanded, the 
base of the petiole is ensheathed by the torn edges of the 
ruptured stipule belonging to an older leaf. The stipules are 
then very clearly seen to be continuous with the stem tissues 
down the flanks of the rhizome. 
The Vascular Skeleton. 
The rhizome is traversed by a single axile stele, in the 
upper face of which narrow triangular foliar gaps occur at 
intervals, one in front of each leaf-trace ; but in the remaining 
portion the vascular cylinder forms a ring enclosing a central 
core of parenchyma in the older stems. It is, however, 
almost solid in the youngest rhizomes. In general character 
the stele recalls that of Botrychium to which it approximates 
more in character than to that of Ophioglossum , with the 
possible exception of O.Bergianum , some specimens of which, 
to judge from one of Bower’s figures 1 of a transverse section 
of the stem, resemble our stem as seen in transverse section ; 
but this aspect of the matter will be considered by-and-by. 
In accordance with the position of the leaves on the 
rhizome, the leaf-traces arise right and left of the middle line 
on the upper surface of the stele. The trace to each leaf is 
single, at least at its origin, and it runs for some little distance 
in the cortex, only diverging from the main stele at a very 
narrow angle before it obviously branches, and these smaller 
strands turn sharply upwards into the petiole. We say 
obviously branches , because, as will be seen later, the trace, 
though apparently single, in reality consists already of at 
least two separate strands which can be readily distinguished 
from each other. 
In the character of its leaf-trace, Helminthostachys more 
1 Bower, Studies in the Morphology of Spore- producing Members : II. Ophio- 
glossaceae. London, i8y6. 
