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.