THREE DAINTY FERNS
Although the members of the family Hymenophyllaceæ are largely tropical,
we are fortunate in having three representatives in the United Kingdom.
Two of these, both Filmy Ferns, are not so familiar to people as they
might be, if folk were only a little more observant; whilst the Bristle
Fern is only to be found in the South of Ireland. All the species require
an abundance of moisture, and they attain their greatest perfection on
rocks which are dripping with water.
_Trichomanes radicans._ The generic name is said to be derived from two
Greek words—_thrix_, “a hair,” and _manos_, “soft”; the specific name is
obviously connected with the Latin _radix_, “a root,” and has reference
to the creeping rhizome. The Bristle Fern.
[Illustration: Trichomanes radicans. The Bristle Fern.]
This species is quite one of the most beautiful of our native species.
Its fronds are very graceful in form, and are of such a delicate texture
as to be almost transparent. The general outline of the fronds is
triangular in shape. The leaves, varying in length from three inches to a
foot, rise from a black, creeping rhizome, which will often cover a large
area on a moist rock with a perfect network. The stipes or bare portion
of the frond is, as a rule, about the same length as the leafy portion. A
singular feature is a wing-like margin which is present on the upper part
of the leaf-stalk. The frond of the Bristle Fern is divided three or four
times, the first of the pinnæ being placed alternately on either side of
the rachis. The pinnules are deeply cut. The veins of the frond are very
strongly marked. All the divisions of the leaf are more or less curled,
so that the frond as a whole presents a curled appearance.
The sporangia of the Bristle Fern are borne of the veins in the lobes of
the fronds. These are produced in curious cup-shaped processes which are
really formed by the margin of the leaf. The veins pass right through
these receptacles and project beyond the outer edges, thus giving a
curious bristly appearance to the frond as a whole.
The Bristle Fern, as has been indicated, chiefly occurs in the South of
Ireland. It has been discovered in several counties, though it seems to
be best established in the Killarney district. Any attempt to cultivate
this Fern will prove a failure, unless the plants are kept continuously
under a close glass cover where the atmosphere is saturated with
moisture. The Bristle Fern is evergreen.
_Hymenophyllum tunbridgense._ The generic name is derived from two Greek
words—_hymen_, “a membrane,” and _phyllon_, “a leaf”; _tunbridgense_ has
reference to the fact that the species was first of all noticed at
Tunbridge Wells. The Tunbridge Filmy Fern.
The fronds, rarely more than two or three inches long, are of a very dark
green colour, and rise from a slender, creeping rhizome which produces
immense quantities of fine roots. The texture of the fronds is of a
delicate nature, and the veins are strongly marked; in colour the leaves
are dark green. The outline of the fronds is roughly ovate; that is, it
tends to be broadest towards the centre. The pinnæ branch alternately
from either side of the rachis, and these are usually very distinctly
lobed. If examined with a magnifying glass it will be seen that the edges
of the pinnules are bordered with bristling points.
In the case of the Tunbridge Filmy Fern, the sporangia are gathered in a
little cup formed by the margin of the leaf; these are present at the end
of the veins which branch out from the mid-veins of the pinnæ.
[Illustration: Hymenophyllum tunbridgense. The Tunbridge Filmy Fern.]
The Tunbridge Filmy Fern has a very wide distribution in this country. As
a rule the plant grows intermingled with moss, and on this account it is
often passed by without recognition. Almost everywhere where there are
wet and especially water-splashed rocks one may expect to find this
species. The Tunbridge Fern can only be cultivated in the same manner as
that indicated in the case of Trichomanes. The plant is evergreen.
_Hymenophyllum unilaterale._ The specific name is, of course, a Latin
word meaning “one-sided”; the application of the term is explained in the
following description. (In some books this species has been called _H.
Wilsoni_, out of compliment to a Mr. Wilson, who is said to have noticed
the species first of all.) The One-Sided Filmy Fern.
Some botanists have considered that the One-Sided Filmy Fern is merely a
variety of the former species, though it is generally considered to be a
distinct type. The two plants often grow mixed up together and
superficially look very much alike; it is only after a close examination
that the differences become apparent. In a general way it will be found
that in the case of the One-Sided Filmy Fern the fronds are somewhat more
narrow than those of the Tunbridge Filmy Fern. The chief point of
distinction is indicated in the popular name:—if the pinnæ are closely
examined it will be seen that the upper portion is much more divided than
the lower side. Another distinctive point to which attention should be
drawn is that in this species the pinnæ show a marked tendency to curve
backwards.
A study of the fertile leaf of the One-Sided Filmy Fern will also give us
an additional point in the identification. With a magnifying glass it is
plainly seen that the margin of the cup-shaped receptacle into which the
sporangia are gathered has not the toothed border to be found in the case
of the Tunbridge Filmy Fern.
As has been indicated, we may look for the One-Sided Filmy Fern in
exactly similar situations to those which suit the Tunbridge Filmy Fern.
The former species is said to be more common in Scotland and Ireland than
the latter. The One-Sided Filmy Fern is, of course, an evergreen.