268 
A. G. Tansley. 
The species of Ophioglossum have closely crowded simple or 
dichotomous leaves and the vascular cylinder of the stem bears the 
same sort of relation to that of Helmintliostacliys or Botrychiuni 
that a simple dictyostele bears to a solenostele in the Leptospor- 
angiate Ferns, i.e., the leaf-gaps overlap, so that in transverse 
section the stem-cylinder appears as a number of collateral bundles 
arranged in a ring (Fig. 95). 1 The leaf-trace, as in the other genera, 
consists of a single strand which starts from the base of a leaf-gap 
(Fig. 92, C), and apparently forks as in the other genera. The leaf- 
venation is reticulate. 
Fig.'95. Ophioglossum vulgatum. Diagrams of transverse sections of stele ; 
A showing one, B two overlapping leaf-gaps. 
The roots of Helminthostachys are usually hexarch (tetrarch to 
heptavch),oi Botrychium triarch or tetrarch, but diarch in B.Lunaria, 
with occasional monarchy apparently by reduction of one protoxylem 
and fusion of the two phloems. In Ophioglossum the roots are 
usually diarch or monarch as in Botrychium Lunaria, though in 
some species triarch or even tetrarch. 
Though the three genera of Ophioglossales probably have no very 
near connexion with one another in descent, it seems that the most 
likely view of their relationship, so far as anatomy is concerned, is to 
regard the three types as on the whole representing a reduction-series, 
starting with Helminthostachys, which itself shows distinct signs of 
reduction in its incomplete and irregular internal endodermis. 
Botrychium may in some respects be regarded as still further reduced, 
e.g., in the complete loss of the internal endodermis in the adult 
plant, and in its endarchy, while its possession of a cambium may 
be a fresh progressive development. Ophioglossum is certainly 
more advanced than the other two from the point of view of its 
“ dictyostelic ” structure. Its actual vascular strands suggest 
reduction, as does the symmetry of the root-stele. 
On the whole, in fact, so far as anatomy is concerned, it looks 
as if evolution had progressed within the group more from the type 
of Helminthostachys to that of Ophioglossum than in the other 
In some cases, however, the leaf-gaps do not overlap. 
1 
