28 
Lady Isabel Browne 
though their ancestors may have been closely allied to the Botryop- 
terideae, they cannot be descended from any known member of the 
latter order. 
The Hymenophyllaceae are clearly but distantly related to the 
Ophioglossaceae. 
Those species of Schizcea in which there is a woody ring 
surrounding a pith resemble Helminthostachys, but this similarity is 
obviously homoplastic, for the stele of Schizcea was clearly derived 
from a protostele within the limits of the Schizaeaceae. Briefly, 
though the Ophioglossaceae show in their stelar structure and the 
frequent dichotomy or dichotomous venation of their fronds certain 
resemblances to the simpler Schizaeaceae, they differ strikingly from 
them in important points, such as the position of the sporangiferous 
part of the frond, the origin and structure of the sporangia, and, 
most important of all, the structure of the prothalius. The two 
orders do not, therefore, appear to be closely related. 
The Gleicheniaceae, Matonineae, Cyatheaceae, Polypodiaceae 
and Loxsomaceae differ even more obviously and widely from the 
Ophioglossaceae. 
In Osmunda we frequently find a ring of endarch xylem bundles, 
separated by medullary rays and surrounded by a ring of phloem ; 
this recalls the structure of Oplrioglossum, though here the phloem too 
is broken up, and is associated in collateral bundles with the xylem. 
In Botrychium and Helminthostachys, however, the phloem remains 
continuous. The mesarchy of the latter genus finds its counterpart 
in Todea. The study of fossil types shows that the Osmundaceae 
are descended from protostelic forms and this is presumably true of 
the Ophioglossaceae. The presence of internal phloem in some 
Osmundaceae and a little secondary xylem in some Adder’s Tongues 
is not an important difference, for these tissues are absent in the 
simpler members of the respective orders. In both orders we find 
multiseriate pitted tracheae, which appear, on comparative grounds, 
to be primitive; further in both orders more than one cell contributes 
to the formation of the sporangium. These characters appear to 
indicate a certain affinity, but the essential difference between the 
radially symmetrical Ophioglossaceous prothalius and the dorsiventral 
one of Osmunda and Todea, and the scarcely less important difference 
that an adaxial sporangiferous branch of the frond is found in the 
one and not in the other order, renders a close affinity between them 
very unlikely. 
/ 
The Marsileaceae appear to be very remote from the Ophio¬ 
glossaceae ; but it is interesting to note that in both the sporangia 
