47 
r Anatomy of the Ophioglossaceae. Ill . 
is comparable to what is found in the Hymenophyllaceae and in some 
Zygopterideae, such as Ankyropteris Grayi. On the other hand, the relation 
of the branch-stele in Helminthostachys to the stele of the main axis, and 
not to that of the subtending leaf-trace, is comparable to what is found in 
some other Zygopterideae, where, however, a relation of the branching to 
a leaf-axil is not established. Thus the branching in Botrychioxylon , Anky¬ 
ropteris corrugata , Diplolabis Romeri , and Metaclepsydropsis duplex is 
described as dichotomous, ‘using the word in the somewhat loose sense, 
which is inevitable when dealing with fossils \ The facts regarding the 
branching of the Zygopterideae have been recently summarized and dis¬ 
cussed by Scott, and it is only necessary to refer to his recent papers. 1 It is 
clear that in this group of plants we meet both with branches standing in 
the leaf-axils and connected with the meristele of the subtending leaf, and 
with branches the steles of which were related directly to the stem. In 
the latter cases, to which the term dichotomy is applied, the two branches 
were sometimes equal, and in other cases the appearance was of a smaller 
stele attached laterally to a main one. Dr. Scott leaves it open whether 
the dichotomy is the more primitive condition, the axillary association with 
leaves being secondary and derived, or whether the dichotomies may be 
really cases of modified lateral branching. The regular presence of dormant 
axillary apices in Botrychium and Helminthostachys appears to be in favour 
of the relation between leaf and branch being part of the primary con¬ 
struction of. these plants. The vascular relations of the branches in 
Helminthostachys are directly with the stele of the rhizome. It is easy to 
see how with greater separation of the branch from its subtending leaf, and 
somewhat stronger development of the branch, a state of affairs would 
result indistinguishable from what is described as dichotomy in some 
Zygopterideae. Were a branch rudiment to develop close to the growing 
point of the rhizome of Helminthostachys , the main rhizome continuing its 
growth, an appearance of equal dichotomy would probably result. 
In any case there is a striking parallel both in the variety in the vascular 
relations of the branches to the main shoot, and in the details of the 
vascular connexions, between the Zygopterideae and the Ophioglossaceae. 
The regular presence of lateral branches or suppressed buds in some of 
these plants must be given due weight in considering the general question 
of whether lateral monopodial branching is primitive or derived from 
dichotomy. The case of the Ophioglossaceae appears to support the 
former view. 
The argument for a relationship of Ophioglossaceae with Zygopteri¬ 
deae is clearly stated and advocated from the side of the extinct plants in 
Dr. Scott’s paper on Botrychioxylon . More detailed study of Helmintho¬ 
stachys strengthens the case for this affinity from the side of the existing 
1 Ann. of Bot., xxvi (1912), pp. 57-60; Trans. Linn. Soc., 2nd ser., Bot. vii. 
