42 
Lang.—Studies in the Morphology and 
Bower, 1 and will not be further discussed here. It is confirmed by this 
study of Helminthostachys. 
Without dwelling on the question of actual relationship of the group, 
some of the main data for comparison afforded by this plant may be 
reviewed, and possible comparisons indicated. In doing this it is necessary 
to extend the field of comparison to some of the Cycadofilices. The main 
features of importance for comparison in the rhizome of Helminthostachys 
are (a) the presence of inner and outer xylem, (b) indications of secondary 
thickening, (c) peculiarities of the leaf-trace, (d) axillary branching and the 
vascular relations of the branch. These may be briefly discussed in order. 
The comparisons indicated are not to be taken as necessarily implying 
actual relationships. 
(a) The distinction of inner and outer primary xylem is, as has long been 
known, exceptionally clear in the large adult rhizomes of Helminthostachys. 
An essentially similar construction has been shown in this paper to hold for 
small rhizomes, where, however, the inner xylem does not consist of pitted 
tracheides; it may be solid or form a mixed pith. The progressive 
elaboration exhibited by the stele of Helminthostachys is particularly 
instructive, as the zone of inner xylem is preserved even in the large 
rhizomes. Thus comparing Helminthostachys with other Ophioglossaceae 
we have an interesting range of variants on a fundamental type of con¬ 
struction. In the one direction we have the Ophioglossum type with 
a reticulum of collateral bundles, consisting of outer primary xylem and 
phloem, all trace of inner xylem having usually disappeared. On the other 
hand, we have the Botrychium lunaria type with only traces of inner xylem 
round the pith, but with a well-marked zone of primary outer xylem passing 
on the outside into the zone of secondary xylem in large stems. In 
other species of Botrychium , e. g. B. virginianum, the radial arrangement of 
the elements of xylem begins at once, so that in this respect no equivalent 
of the primary outer xylem of B. lunaria or Helminthostachys is recog¬ 
nizable. In the species of Botrychium we find the same problem of what is 
to be regarded as primary xylem that faces us in the higher Gymnosperms. 
The same general direction of elaboration of a monostele appears to have 
been followed independently in several lines of Filicales, and in the 
Lyginodendreae, while parallels can be traced in other groups such as 
the Lepidodendreae. 
As to how far the distinction of inner and outer xylem can be usefully 
followed in the Filicales, cannot be discussed here. Among existing Ferns 
it is clearly seen in such forms as the Gleicheniaceae, and the same line of 
interpretation can be applied to the Schizacaceae, where the elaboration is 
in many respects parallel to the Ophioglossaceae. The distinction is also 
1 Handworterbuch der Naturwissenschaften (1913), Bd. iii, p. 935. The full statement of the 
alternative view of a relationship to the Lycopodiales is in the Land Flora (1908). 
