HOW TO KNOW
THE FERNS
BY
S. LEONARD BASTIN
WITH THIRTY-THREE ILLUSTRATIONS
METHUEN & CO. LTD.
36 ESSEX STREET W.C.
LONDON
_First Published in 1917_
CONTENTS
CHAP. PAGE
I. The Ferns and their Allies 1
II. Life Histories 13
III. Yesterday and To-day 23
IV. Three Dainty Ferns 33
V. The Bracken Fern and Two Interesting Species 38
VI. The Male Fern and its Relatives 46
VII. The Lady Fern and the Spleenworts 66
VIII. The Polypodies 86
IX. The Royal Fern 93
X. Four Curious Ferns 96
XI. The Club Mosses 101
XII. The Horsetails 112
XIII. Fern Collecting and Preserving 122
XIV. The Culture of Ferns 129
Index 133
LIST OF ILLUSTRATIONS
PAGE
The Bristle Fern 34
The Tunbridge Filmy Fern 36
The Bracken Fern 39
The Maidenhair Fern 42
The Maidenhair Fern (Enlarged view of Back of Frond) 43
The Male Fern 47
The Mountain Buckler Fern 51
The Mountain Buckler Fern (Enlarged) 52
_Nephrodium dilatatum_ 54
The Holly Fern 58
The Oblong Woodsia 62
The Brittle Bladder Fern 64
_Athyrium filix-fæmina_ 67
The Rue-leaved Spleenwort 71
The Rue-leaved Spleenwort (Enlarged Back of Frond) 72
The Sea Spleenwort 76
The Maidenhair Spleenwort 79
The Green Spleenwort 81
The Hartstongue 82
The Sori on the Back of a Hartstongue Frond 83
The Common Polypody 87
Enlargement of the Sori on the Frond of Common Polypody 88
The Beech Fern 89
The Royal Fern 94
The Adder’s Tongue 97
The Moonwort 99
The Common Club Moss 102
The Fir Club Moss 104
The Quillwort 108
_Azolla caroliniana_ 110
Barren Stem of _Equisetum arvense_ 113
Fertile Cones of _Equisetum maximum_ 115
The Dutch Rush 120
HOW TO KNOW THE
FERNS
CHAPTER I
THE FERNS AND THEIR ALLIES
In its lowest forms vegetable life is a very simple affair. The minute
Algæ which clothe damp surfaces with a green film show few indeed of the
characteristics with which we are familiar in the higher plants.
Certainly they are green, proving that the tiny cells of which they are
composed contain the wonderful colouring matter—chlorophyll, by means of
which they are able to assimilate carbon from the carbonic acid of the
air. There is, however, in these lowly plants no sign of a stem, a leaf,
or a root. As we ascend in the scale of vegetable life we begin to get an
increasing number of distinctive characters. In the case of the Mosses we
have plants with distinct stems and leaves. But Mosses have no true
roots, neither is there any vascular (woody) tissue in their composition.
Mounting yet higher in the scale we come to a very important and
interesting group of plants usually referred to as the Vascular
Cryptogams. In this group are included the Ferns, the Horsetails, and the
Club Mosses. In passing, it may be pointed out that the term Cryptogam is
a name which was originally given to the flowerless plants by Linnæus to
indicate that the plan of fertilization was hidden. The name is still
retained, but it has lost its meaning in this sense, in that since the
introduction of high-power microscopes it is not necessarily more
difficult to study the fertilization of the non-flowering plants than it
is to watch the process in the kinds which bear blossoms.
A small acquaintance with the Vascular Cryptogams will show us that they
approach very closely to the flowering plants, or Phanerogams, as they
are called, in their general features. It is true that in the cases of
the Club Mosses and Horsetails the leaves are small or very poorly
developed, but with the Ferns the foliage is often of an advanced type.
All the Vascular Cryptogams, apart from a few insignificant exceptions,
produce real roots; and, as the name implies, in a botanical sense,
evidence woody tissue in their composition. Whilst the Club Mosses and
Horsetails are comparatively humble plants, the Ferns have reached a
remarkable development in the arboreal species. These, of course, grow
into large trees which may be fifty or more feet in height, with thick
woody trunks. Our common Male Fern not infrequently forms a short
trunk-like stem if it is allowed to remain in an undisturbed state for a
number of years. Not all the Ferns are large or even of moderate size;
many of the Filmy Ferns are so minute that they are often taken for
Mosses by those who do not know any better.
All the Vascular Cryptogams show an alternation of generation; that is,
in the life history of each plant there is a sexual and an asexual
individual. As is fully explained later, the plant which arises from the
spore of the Vascular Cryptogam is quite an insignificant body known as
the prothallus. This has a comparatively short existence in most cases.
It is on the prothallus, however, that the sexual organs are produced,
and after fertilization the plant as we know it arises. This individual
is called the sporophyte. The plant is responsible for the spores which
are produced in little cases called sporangia. These are borne straight
on the leaves, and are produced without anything in the way of
fertilization having taken place. As far as the Ferns are concerned, the
spores are all of one kind, but in certain of the Club Mosses two kinds
of spores are produced.
Apart from a few exceptions the Vascular Cryptogams are mostly perennial
in habit. In many cases other means of reproduction are available than
the agency of spores. It is believed that the Bracken Fern is rarely
reproduced by its spores. The increase of this plant seems to be very
effectively carried out by means of the strong growing underground stems
which shoot about in all directions. The Horsetails commonly propagate
themselves in the same way, and it is this which makes them so difficult
to eradicate in the garden. In the case of many Ferns a common mode of
increase is that of budding off new plants on the leaf. The well-known
New Zealand species, _Asplenium bulbiferum_, produces little buds on its
fronds; these grow into small plants, so that each leaf may be
responsible for dozens of new individuals. An even more singular case is
the so-called Walking Fern from North America (_Scolopendrium
rhizophyllum_), which bears long, tapering leaves something like our
Hartstongue. These bend over in such a way that their tips touch the
ground; on the point of the frond a bud is developed. Roots go down into
the soil from the point of the frond, leaves shoot upwards, and thus a
new plant is born. In some species of Club Moss the increase of the plant
by spore production is supplemented by a plan which involves the bearing
of bulbils on the shoots. These are vegetative processes which give rise
to new individuals when they tumble to the ground.
It is of interest to consider the general characteristics of the members
of the Fern tribe. As a rule the stem is either in the nature of a short
underground process bearing a rosette of leaves, as in the case of the
Male Fern and Hartstongue, or there is a horizontal stem more or less
below the surface of the soil, such as is to be seen in the case of the
Bracken Fern and the Polypody. Sometimes the stem assumes the proportions
of a trunk, but these Tree Ferns only occur in the tropics. Where the
stem of the Fern is upright it is properly termed a caudex, whilst in its
horizontal form it is spoken of as a rhizome. There is actually some
doubt as to the real nature of the frond of the Fern. Some botanists are
inclined to believe that it is not really a leaf at all, but is a
modified stem structure. Those who hold this view consider that the
curious scaly structures so common amongst Ferns are really the leaves of
the plant. Here the matter must be left on the present occasion, as it is
proposed to use the terms leaf and frond as meaning the same thing.
An outstanding feature in the case of most Ferns is the remarkable manner
in which the fronds are subdivided. In the case of the Male Fern it is
seen that the upper part of the stalk, or rachis, as it is called, bears
two rows of leaflets. These leaflets are properly referred to as pinnæ.
When the leaflets are subdivided the divisions are spoken of as pinnules.
These pinnules may be deeply lobed, and when this is the case each lobe
is called a segment. In very large fronds the pinnules are again divided;
the frond is then said to be tri-pinnate. Sometimes towards the top of
the pinnæ or the frond the divisions become less pronounced; this
character is designated pinnatifid. It should be noticed that the lower
portion of the stalk, on which there are no pinnæ, is called a stipes. Of
course in some cases, as with the Hartstongue, the leaf is quite
undivided, without even any very pronounced indentations on the margin.
The unrolling of the Fern frond is a very beautiful process. Where the
leaf is not divided in any way the process of expanding resembles the
uncoiling of a watch-spring. Even where there are divisions the unrolling
goes forward in the same manner with each subdivision, even down to the
lobes. This particular mode of unfolding is called circinate. The texture
of the leaves of Ferns is mostly thin and delicate, so that apart from
some exceptions the foliage is not able to withstand the action of dry
air. A notable feature with a large number of Ferns is the length of time
which the leaves take to develop. The fronds of the Male Fern, for
instance, start in the bud at least two years before they actually
unfold. An examination will show that the roots of the Male Fern spring
from the frond bases. It will be found that the position of the roots is
the same in all Ferns.
With all Ferns the production of spores is confined to the leaves. In
many instances there is no distinction between the fertile and the barren
leaves. The stem does not start at once to produce leaves bearing the
sporangia or spore cases. Thus, in the very young Fern the fronds are
always barren; as the stem becomes older, fertile fronds are produced. In
some cases the sporangia are borne on distinct leaves, as in the case of
the Hard Fern, or on special parts of the leaves, in the manner to be
seen in the Royal Fern. The difference in such cases is not really a very
important distinction. A careful examination of the fertile portion of a
Royal Fern frond will show a small amount of green tissue, or mesophyll,
as it is called, at the lower portion of the pinnæ. Actually the fertile
leaf, or part of a leaf, is similar to the barren portions, save that it
produces a much reduced amount of green tissue or, in some cases, perhaps
none at all.
In general appearance the Club Mosses bear a resemblance to the true
Mosses, and hence the popular name, which is certainly rather misleading.
With these plants the leaves are small and almost bristle-like, and are
gathered closely round the stem. In many of the Club Mosses a large part
of the stem lies closely along the ground, and from this at intervals
roots are sent down into the soil and leafy shoots rise upwards. The
sporangia are produced on special leaves, which are usually gathered
together in the form of cones.
Although they vary somewhat in size, all the Horsetails are striking
plants. Here there is a branching underground rhizome from which arise
the aerial stems. The most distinctive feature of the plant are the
whorls of smaller branches which arise from the joints of the main stem.
These carry on the work which is usually assigned to the foliage of the
average plant,—that is, the assimilating of carbon from the carbonic acid
of the atmosphere. The real leaves of the Horsetail are much reduced in
size, and take very little part in the work of nutrition. We shall find
them at the joints of the stem as rings, each collection forming a kind
of sheath. The leaves, which are usually of the same number as the
branches, show no sign of their individuality, save in the little
projecting teeth. In some species the fertile shoots, which appear in the
form of cones, are produced specially. These appear in the spring before
the ordinary vegetative growths, and are quite destitute of chlorophyll.
In other species the normal green shoots are fertile at the termination.
The sporangia are borne on curious scale-like leaves, a large number of
which go to the making of a cone.
One or two aquatic plants, which belong to the Vascular Cryptogams, call
for comment. The Pillwort is a singular plant not uncommon in damp
situations. The leaves of this plant are narrow, and the spores are
produced in curious rounded processes. The Water Fern (_Azolla_) is an
introduced plant which sometimes grows abundantly on lakes in the South
of England. Both the before-mentioned plants are allied to the Ferns. The
Water Club Mosses (_Isoëtes_) are represented in this country by a
species commonly known as the Quillwort. This plant grows in lakes, and
is easily recognized by its quill-like foliage.
Owing to the large number of species a somewhat elaborate classification
is necessary in the case of Ferns. In distinguishing the different
families, the manner in which the collections of spore cases, known as
sori, occur, as well as the features which the individual sporangia
present, are important guides. The actual position of the sorus on the
leaf, the presence or absence of a covering (indusium), are also
distinctive features, both in the families and sub-families. When the
individual sporangium is examined it is found that there is often present
an annulus, a special ring of cells which plays an important part in the
rupturing of the case. The extent of this ring or (as sometimes happens)
its absence will alike be a decisive factor in fixing the family to which
a species belongs. In some families a prominent feature is the fact that
the sporangium has little or no stalk, although this is the exception
rather than the rule. For a more complete description of the sporangium
of the Fern the reader is referred to a succeeding chapter. It is
certainly helpful to a study of these beautiful plants to try to fix in
the mind the families, and their characters, of the order _Filices_. In
all there are eight families belonging to the Fern tribe. These are given
in the order in which they occur in technical books.
1. _Hymenophyllaceæ._—The Filmy and Bristle Ferns. This family includes
some of the simplest kinds of Ferns. There are only three representatives
in the United Kingdom. These are _Hymenophyllum tunbridgense_, _H.
Wilsoni_, and _Trichomanes radicans_. The two former species are fairly
common on rocks which are splashed with water, but the latter seems only
to occur in restricted districts in the South of Ireland. All the species
must have an abundance of water, or the foliage quickly shrivels. This is
due to the fact that the leaves consist of a single layer of cells and
are, of course, very thin. A distinctive feature in this family is the
bearing of the sporangia; these are almost or entirely stalkless. The
sorus, as the group of sporangia is called, is surrounded by an enclosure
from the leaf margin. In _Trichomanes_ this is cup-shaped, whilst in
_Hymenophyllum_ it is bivalved. The popular name Filmy Fern—bestowed on
the Hymenophyllums and allied species—has reference to the
semi-transparent nature of the fronds. In the case of _Trichomanes_ the
axis on which the sporangia are inserted often projects beyond the cup in
which they are contained. This gives a curious spiky appearance to the
fertile frond, and hence the name Bristle Fern.
2. _Polypodiaceæ._—This is a very large family, containing two or three
times as many species as all the rest of the Vascular Cryptogams put
together. Nearly all our native species, with a few exceptions, belong to
the family. A distinctive feature is the incomplete annulus of the
sporangium. Another point to notice is that the spore cases are stalked.
So large is the family that it has been divided into a number of
sub-families; the members of these are chiefly characterized by the
position of the sorus, the cluster of sporangia on the back of the frond.
The different sub-families may be briefly outlined.
(_a_) _Davalliaceæ._—There are no British representatives of this family.
In this case the sorus is always near to the margin of the leaf, and the
indusium or covering is cup-shaped. A familiar species is _Davallia
bullata_ from the East; the rhizomes of this Fern are trained into
various shapes by the Japanese.
(_b_) _Pterideæ._—The Bracken Fern (_Pteris aquilina_), the Maiden Hair
(_Adiantum capillus-veneris_), and the Parsley Fern (_Cryptogramme
crispus_) belong to this sub-family. A notable feature of the Bracken is
the continuous marginal sorus. There is no proper indusium, but the leaf
margin curls over and protects the sporangia to some extent.
(_c_) _Aspidieæ._—The sorus is in the form of a little rounded heap. The
indusium, which is usually kidney-shaped, is supported by a central
stalk, somewhat after the manner of a nasturtium leaf. The Male Fern
(_Nephrodium filix-mas_) belongs to this sub-family, as well as the
Bladder Ferns (_Cystopteris_) and the _Woodsias_.
(_d_) _Asplenieæ._—Here the sorus is elongated or linear. The indusium
arises from a vein to which the sorus is attached. Some very charming
Ferns belong to this sub-family. Many botanists include the Lady Fern
(_Athyrium filix-fæmina_) in this section. Certain of the Spleenworts
(_Asplenium_) are common. The Wall Rue (_A. ruta-muraria_) and the Black
Maidenhair Spleenwort (_A. adiantum-nigrum_) are well known.
(_e_) _Polypodieæ._—The sori on the underside of the leaves are without
any indusium. They are in rounded clusters, and look like small buttons.
_Polypodium vulgare_ is one of our commonest Ferns. Some of the other
species of this genus, such as the Oak Fern (_P. dryopteris_) and the
Beech Fern (_P. phegopteris_), are abundant in some localities.
(_f_) _Grammitideæ._—The Gold and Silver Ferns. The only British species
is the Annual Maidenhair (_Gymnogramma leptophylla_). The plant occurs in
the Channel Islands. This species is one of the few Ferns which are not
perennial. The sori, which follow the veins, have no indusium.
(_g_) _Acrosticheæ._—There are no British representatives of this
sub-family. In this case the whole of the underside of the leaf is
covered with sporangia, and there is no indusium.
3. _Cyatheaceæ._—There are no British representatives of this family,
which is interesting, owing to the fact that it includes the Tree Ferns.
4. _Gleicheniaceæ._—A group of Ferns which are almost entirely tropical.
5. _Schizæaceæ._—Another tropical family.
6. _Marattiaceæ._—A family of large and handsome Ferns, the members of
which occur in the tropics. There are not many representatives of this
family nowadays, but remains in the Coal Measures show that the species
were very much more numerous in Palæozoic times.
7. _Osmundaceæ._—A small family, but rather an important one, owing to
the fact that a leading representative, the Royal Fern (_Osmunda
regalis_), is so well known. In this species only the upper portion of
the leaf is fertile. The sporangia have very short stalks, and are not
provided with an annulus at all. They burst open in a longitudinal slit,
opposite to a special group of cells just below the apex. The sorus has
no indusium.
8. _Ophioglosseæ._—This family is represented by three British species,
of which the Moonwort (_Botrychium lunaria_) and the Adder’s Tongue
(_Ophioglossum vulgatum_) are best known. There is much doubt as to
whether this family can be properly included amongst the Ferns at all. We
may here give them the benefit of the doubt. The leaves in these species
are unfolded from the sides—a totally distinct plan from that to be
observed in all the Ferns which have been described, where the frond and
its divisions are unrolled upwards. The prothallus is a small underground
body destitute of chlorophyll. The fertile leaves are distinguished from
the barren ones by the production of a special branch which bears the
fructification. The sporangia are large.
The next order of the Vascular Cryptogams is of comparatively small
importance as far as the present study is concerned. It is known as the
_Rhizocarpeæ_ (Pepperworts). The order is divided into two families as
follows:—
1. _Salviniaceæ._—The only two genera are Salvinia and Azolla; the latter
has been already mentioned.
2. _Marsiliaceæ._—The British example is the Pillwort (_Pilularia
globulifera_).
The Club Mosses have been divided into six families. Two of these—the
_Lepidodendraceæ_ and the _Sigillariaceæ_—are only represented by
fossils; and one, _Psilotaceæ_, has no British representatives. The
remaining families all include one or more species which are indigenous
to our islands.
1. _Lycopodiaceæ._—These are the Club Mosses proper. Several species of
the genus _Lycopodium_ are British. The Common Club Moss (_Lycopodium
clavatum_) is often abundant on high moors.
2. _Selaginellaceæ._—A large family containing three or four hundred
species, only one of which, however, is British; this is _Selaginella
spinosa_.
3. _Isoëtaceæ._—A family of aquatic Club Mosses. The British species is
_Isoëtes lacustris_, a plant which is sometimes common in the northern
lakes.
With this brief survey of the Vascular Cryptogams one may naturally pass
to a somewhat more detailed consideration of the life histories of these
interesting plants than it has been possible to give in an opening
chapter.