39 
Anatomy of the Ophioglossaceae. III. 
the same distinctions can be drawn so far up as the procambial strand 
exhibits any lignified elements. PL III, Photo 53 shows a transverse 
section of a stele at this level; the outline of the procambial cylinder can be 
traced, and in it two groups of protoxylem elements are lignified; one of 
these marked l.t. corresponds to the leaf-trace supplying the youngest 
developing leaf, while the other ( px.v .) is the early formed xylem of the 
ventral segment. A corresponding independence of the ventral region of the 
xylem has been traced to close behind the apex in a number of small 
rhizomes. 
We are now in a position to consider the divergent views expressed by 
previous investigators of Helminthostachys , as to the evidence for or against 
the stele, or a portion of it being cauline. 
According to the work of Farmer and Freeman 1 on adult rhizomes, 
the stele can be followed to the apex of the stem beyond the youngest 
leaves and roots, and hence is cauline. These investigators further empha¬ 
size the evidence afforded by the ventral side of the dorsiventral rhizome, 
from which leaves are absent, while the vascular tissue can be traced up to 
the apical meristem. With this view, according to which there is a stem 
with a stele which in part at least is strictly cauline, I am in essential 
agreement. 
Campbell, who has investigated the question mainly on young plants, 
a number of which he describes in some detail, comes to a very different 
conclusion, which will be clear from two quotations, remembering that he 
takes as his starting-point ‘the single axial strand of collateral structure 
throughout cotyledon and root ’, as found in the young plants of some 
species of Ophioglossum. From such strands he derives directly the dictyo- 
stelic arrangements in Ophioglossum and Marattiaceae. After considering 
these he continues : 2 4 The second type of skeleton is that found in Botrychium 
and Helminthostachys . This is a solid, hollow cylinder, with inconspicuous 
leaf-gaps, resulting from the union of the broad leaf-traces which fuse 
completely to form this hollow stele. That the cylindrical bundle, or 
siphonostele, is not due to the formation of a pith within the protostele 
is clearly shown by the development of the bundle in the young sporophyte 
of Botrychium , where it can easily be seen that the component bundles are 
separate at first, and that the pith, so called, of the siphonostele is merely 
a portion of the ground tissue that is included between them, and which 
later becomes entirely separated from the cortical tissue. A similar con¬ 
dition of things may be found in tracing the development of the vascular 
cylinder in the young stem of Helminthostachys .’ 
In describing the structure near the tip of the young rhizome of 
Helminthostachys , Campbell says 3 earlier in the same work: 4 From this 
study of the development of the leaf-traces, following them from the stem 
1 Loc. cit., p. 428. 2 Loc. cit., p. 214. 8 Loc. cit., p. 78. 
