428 Farmer and Freeman . — On the Structure and 
As regards the steles which are given off to the roots, 
one fact becomes immediately prominent, viz. that there 
is no regular connexion between them and the leaf-traces. 
They spring from the lower part of the flanks or from the 
ventral surface of the stele, and never arise in connexion with 
either the leaf- traces or the margin of the foliar gaps. Their 
irregular distribution is equalled by the lack of uniformity in 
their number ; sometimes two or even three root-strands are 
found to be given off between a single pair of leaves. 
This irregularity was pointed out by Prantl 1 ) who rightly, 
as we think, criticized Holle’s attempt to show that a definite 
relation could be made out in Botrychium . At least we have 
not succeeded in confirming Holle’s account, and moreover 
his own figures do not seem to lend much support to his 
contention. 
The rhizome-stele itself can be followed up to the apex 
of the stem beyond the youngest leaves and roots, and hence 
it is cauline in nature, and differs in this respect from what is 
stated by Holle to be true for other Ophioglosseae. There 
can, however, be no doubt as to the condition of matters in 
Helminthostachys , for the dorsiventral structure obviates some 
of the difficulties which meet one in dealing with radial stems. 
The vascular tissue can be traced on both the upper and the 
lower surface (from which leaves are absent) quite up to the 
apical meristem, and, as will be seen later, the actual differen- 
tiation of tissue begins to set in just behind the apex. 
Histology. 
The Rhizome . A transverse section of the creeping stem 
shows an ill-defined dark-coloured peripheral band composed 
of a few cell-layers in thickness which serves to protect the 
inner tissues. On the upper surface, and starting in connexion 
with the bases of the cast-off leaves, the cells grow out some- 
what and undergo periclinal divisions resulting in the formation 
of an irregular layer resembling cork. But this formation 
1 Prantl, loc. cit. 
