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Genus IV. LASTREA, Presl.
One group of the Eerns were formerly called Aspidiums,
or Shield-Eerns. This group, so far as English species are
concerned, is now divided into three, bearing the names of
Lastrea, Polystichum, and Cystopteris. The Lastreas are
known among these by having the indusium, or seed-cover,
round in outline with a lateral notch, thus becoming
kidney-shaped; they are attached to the frond by the
notched part. This group includes some of the largest and
most common of onr native species, and nearly all of them
are remarkable for their elegance. Several of them retain
their fronds through the winter in sheltered situations, but
they are not strictly evergreen, and in exposed situations are
always bare during winter.
Of the Lastreas eight British species are usually recognized,
but the number varies according to the value put
upon certain differences in the plants, by different authors.
The name Lastrea commemorates a zealous botanist and
microscopical observer, M. Delastre of Chatelleraut.
L a st r ea cristata, Presl.—The Crested Eern. (Plate
VI. fig. 2.)
This is the simplest of the British forms of a group of
species intimately related to each other, and which are sometimes
in the aggregate called Crested Eerns; the latter
name is, however, more usually applied only to L. cristata,
of which we have used it as the equivalent. The group
alluded to consists of L. cristata, uliginosa, spinulosa,d%latata
in its many forms, and fmnisecii or recurva, plants which
form a closely connected series, so close, indeed, that some
very eminent botanists consider them as all belonging to
two species only, cristata and dilatata, the other forms being
considered as mere varieties. This view of the subject is, we
believe, almost exclusively confined to those whose lot it has
been to study the Eerns in a general way; and the magnitude
of the subject in such a form necessarily leads to generalizations,
and the acknowledgment only of such dffierences as are
the most obvious. It is, in fact, often inconvenient for the
general botanist to search after or take cognizance of very
minute differences. Those, on the other hand, who study
a smaller series, confined to certain geographical limits—
our own country, for example—being unperplexed by the
magnitude of their subject, as necessarily search for and
find differences of another kind, less obvious at the first
glance, but to be found if looked for; and these, when
proved to be constant and unvarying, are relied on as proper