240 Lang. — Studies in the Morphology and 
a continuation outwards of the centripetal xylem of the stem. The facts 
seem more satisfactorily explained by regarding the leaf-trace not as mesarch, 
but as completed by an adaxial extension of the centrifugal xylem. This 
view is supported by those cases in Helminthostachys in which a truly 
mesarch trace is completed adaxially ; in such cases the two xylems can be 
clearly distinguished. The Ophioglossaceous leaf-trace on this view would 
present points of resemblance to the early departing trace in Zygopterideae 
and to the trace in the Hymenophyllaceae. It would also resemble that 
of Osmunda. Such a view agrees in general with Kidston and Gwynne- 
Vaughan’s interpretation of the C-shaped leaf-trace in the Ferns, but since 
it regards the xylem of the trace (whether solid or tubular) as composed of 
centrifugal xylem extended round adaxially, and not as mesarch, it differs 
in some respects. On this view the hooks of xylem at the outer margin of 
the leaf-trace would be the last indication of the adaxial extension of the 
xylem. 
The derivation of the vascular supply to axillary branches from the 
adaxial xylem of the subtending leaf-trace supports this comparison of the 
leaf-trace with those of the Hymenophyllaceae and Zygopterideae. Further 
facts are necessary before the variations in the vascular supply to the branches 
in Botrychium can be fully elucidated. In essentials, however, the comparison 
of the axillary branching in Ophioglossaceae, Hymenophyllaceae, and Zygo- 
pterideae is strengthened by the vascular relations in B. Lunar ia. The 
Ophioglossaceae may throw light on the variable position of the branches, 
whether on the stem or the subtending leaf-trace found in the Zygopterideae. 
These remarks will indicate, without entering into details, the general 
bearing of some of the additional features in the anatomy of B. Lunaria 
which have been described in this paper. A deeper analysis of the con- 
struction of the rhizome is necessary before such questions as the distinction 
of stem and leaf in its composition can be discussed. The stelar structure, 
the medullation, the construction of the leaf-trace, and the nature of the 
branching are all consistent with a relationship of the Ophioglossaceae to 
the ancient Fern stock, the general features of which are indicated in the 
relatively primitive groups of Ferns, such as Zygopterideae, Botryopterideae, 
Osmundaceae, Hymenophyllaceae, &c. The facts do not appear to point 
to a direct relationship to any particular known group. In any case it 
seems at present more important to elucidate the comparative morphology 
of these more ancient Ferns in all its details than to speculate on the 
problem of actual relationship. 
