venules branch out, these being usually forked, and both
branches bearing a sorus half-way between the margin and
the midvein. The sori, which are thus pretty numerous,
often become confluent, and are partially concealed by the
bent-back margin. The indusium, or cover of the spore-
cases, is in this species small and thin, and is soon thrown
off, and lost.
The Marsh Fern has a wide geographical range, and in
England and Wales occurs in numerous localities; in Scotland
and Ireland it is rather uncommon.
Not a very attractive species for cultivation. It has
been severally referred, under the individual name of Tliely-
pteris, to the families of Aspidium, Polypodium, Acrostichum,
and Polystichum, by various botanical writers.
Genus XVII. OPHIOGLOSSUM, Unnaus.
T h is is very nearly related to the Moonwort, though at first
sight having a very different aspect. The points in which
it agrees, are, that the parts are folded up straight in the
incipient state, and the fronds are two-branched, one branch
being leafy, the other fertile. Ophioglossum differs from