Fig. 67. Adiantum Capillus-Veneris.
Fig. 67. Adiantum Capillus-Veneris.
Fig. 67. Adiantum Capillus-Veneris.
The Acrosticheæ are among the most remarkable offerns in having the whole under-surface of the frond indiscriminately covered with naked sori, and in a few species the upper-surface also. They are situated on the veins and veinlets, from whence they extend into the interstices of the fertile fronds, which are sometimes much contracted. The species are almost all tropical or subtropical. A New Zealand species of Lomariopsis climbs high trees by means of its stout rooting caudex, and has different leaves on different parts of the plant.
The Cyatheineæ are chiefly arborescent ferns, and, with the exception of some fossil species, contain the noblest representatives of the cryptogamic flora. Their fructification consists of dot-like sori, in which the usually compressed oblique sporangia are placed on an elevated receptacle, which forms a raised point on the surface of the fronds when the sporangia are removed. Of these the Alsophileæ are without true indusia, while the Cyatheæ have a spherical indusium, bursting above or below, and forming a cup round the sorus. The pulpy substance of the stem of Cyathea medullaris was a common article of food with the New Zealanders.
The Gleichenineæ have a creeping or climbing rhizome, and globose or trigonal sporangia, few in number, and disposed in a radiating manner, so that the narrow end is internal. They are often seated in a little cavity, and are highly deciduous. The fronds are generally forked or trifid, the middle division being sometimes supplied with a little bulb-like body. They are mostly tropical or subtropical plants, but some species grow in Chili, New Zealand, and Japan.
The Trichomanineæ are pretty well distinguished from other ferns by their pellucid membranaceous texture. As regards their technical characters, they have an oblique and complete ring to the sporangia, which are of a lenticular form, and are collected about a more or less elongated receptacle, which is free within either anurn-shaped cup or a two-valved indusium, projecting from the edge of the frond. They are chiefly inhabitants of the moist tropical forests, or extra-tropical regions of damp and mild temperature. Great Britain only owns one species of the genus Trichomanes, and two of the genus Hymenophyllum, while species of these two genera constitute one-fifth of the fern vegetation of our antipode islands of New Zealand. It is more than doubtful even that the Trichomanes radicans, or Bristle fern, is indigenous, as it is found in no other part of Great Britain except the Irish counties of Cork and Kerry, growing on dripping rocks and waterfalls, or depending from the walls and roofs of caverns; and as it is also found in the West Indies and the North Atlantic islands its transit may be accounted for, as in other cases.
Fig. 68. Trichomanes radicans.
Fig. 68. Trichomanes radicans.
Fig. 68. Trichomanes radicans.
The fronds of the Bristle fern, Trichomanes radicans, are somewhat deltoid, or of a more elongated form, flimsy, and beautifully reticulated when viewed with a microscope. They rise at intervals from a creeping rhizome, bristly, with narrow articulate scales, which often covers the most precipitous rocks on which it grows with a dark-coloured network. The rachis is branched and rebranched three or four times, and the whole being distinctly winged on both sides in the plane of the frond, the successive branches and branchlets running through the leafy part become the veins of those parts, so that a segment of the frond is merely a winged vein, the wings on the branches being however broader than those on the rachis. The veins, which divide alternately, are hard, woody, and wire-like, and, when barren, terminate before reaching the ends of the segments; but, when fertile, they extend beyond the segment, the tissue of which separates and distends in the form of a more or lesselongated cup around the prolonged vein. At the base of that vein the sporangia form a small globular cluster; and, as they advance towards maturity, the vein extends in the form of a bristle, far beyond the mouth of the cup (fig. 68). The cup is winged in the more luxuriant form of the plant, in consequence of the double layer of tissue composing the segment to which it belongs not separating through its whole breadth. The cup-like cylinder being slightly compressed in the plane of the frond is indicative of its origin.
Fig. 69. Hymenophyllum tunbridgense.
Fig. 69. Hymenophyllum tunbridgense.
Fig. 69. Hymenophyllum tunbridgense.
A slight difference in fructification separates the Hymenophyllum tunbridgense, or Film fern (fig. 69), from the Trichomanes, for both have a creeping rhizome, from which single fronds spring at short intervals. The leafy parts of the fronds are merely winged veins, and the wings consist of two layers of cellular tissue finely reticulated. The Hymenophyllum is distinguished from the Trichomanes by a two-valved cup spinously serrated, which completely conceals the fruit-bearing vein, while, in the Trichomanes, the cup is more cylindrical, smooth-edged, with the fertile vein projecting far beyond it (fig. 68). The beautiful little Film fern, with its semi-transparent fronds not more than two or three inches high, grows on shady wet rocks, among the moss on the branches and roots of old trees, and on the ground near lakes and rivulets. It is hardy enough to live in the Highlands of Scotland; but the H. unilaterale, a far less beautiful plant, has its limit in Unst, the most northern of the Shetland Islands. The fructification in the latter plant, though the same in position, is stalked instead of being sessile. The involucre is rounded andovate, instead of being cup-shaped, with much swollen convex valves, meeting by their edges but not compressed towards the apex.
The Schizæineæ are many of them climbing ferns, and for the most part tropical. Lygodium articulatum climbs trees in New Zealand to the height of fifty or one hundred feet, and its tough wiry stems are used for cordage. In one group of this order, represented by Lygodium, the sporangia are disposed at the back of the frond in imbricated marginal spikes, formed by a transformation of the ultimate pinnæ. In the other division, represented by Schizæa, the fruitful spikes are really on the under-side of the frond, but the frond being reversed they seem to be on the upper.
The Ceratopteridineæ, sometimes called Parkeriaceæ, are tropical aquatic ferns, whose sterile fronds, which are membranaceous, with a thick vascular footstalk, float on the surface of the water, and by the time these are nearly decayed the fertile fronds are perfected. The latter are more erect, repeatedly divided and forked, the divisions being linear. There is only a single genus, Ceratopteris, which has continuous sori occupying the longitudinal veins at the edge of the frond, and covered by the indusioid margin. The sporangia have a very broad incomplete ring, and connect the ringless ferns with the group which possess them. The spores are triangular, and marked with three sets of concentric ridges.
The order Osmundineæ contains the Osmunda regalis, considered to be the finest of all European ferns, which is common throughout Great Britain in wet spongy soils, and appears to be the only species of the group that is European. The fronds grow in tufts from a thick woody caudex, which branches and extends widely by the formation of lateral crowns, but, if impeded, it elongates and rises in an erect position to the height of twoor even three feet above the soil. The barren fronds of the large luxuriant tufts are highly developed, and are from six to nine or even eleven feet high; the fertile fronds are shorter and fewer in number. The bipinnate character prevails throughout; the primary divisions are opposite, the secondary alternate, and the pinnules are oblong and opposite. The sculptured sporangia have a very rudimentary ring, and, in the fruit-bearing fronds, four or five of the lower pairs of pinnules have the leafy character, while the remainder develop clusters of sporangia in place of pinnules. The sporangia on the fruitful branches are at first pale green, but gradually become reddish brown, hence the name of Flowering fern. The Leptopteris section of the genus Todea, almost peculiar to New Zealand, has beautiful transparent fronds, with naked sporangia placed upon the veins, forming very much scattered sori.
TheMarattiaceæmay be partly known by their huge globose rhizome projecting above the ground, and rough with the processes from which the leaf-stalks have fallen. This sends out a few large fibrous roots, and consists of cellular tissue abounding in starch, with small bundles of fibro-vascular tissue regularly distributed through it. The stipes have a pair of stipule-like organs at their base; and the sori are either oblong fronds of a double row of sporangia, which in some cases is concrete, or they are circular with the sporangia annularly concrete, or they are connate throughout the fertile portions. These peculiarities respectively distinguish the smaller groups of Marattineæ, Kaulfussineæ, and Danæineæ, while the group Marattiaceæ itself is distinguished from Ophioglossaceæ by having its sori dorsal, that is, set on the back, or under-surface, of flat leafy fronds. The leaves of Angiopteris evecta are usedas a perfume in the Sandwich Islands, and its rhizome serves for food, as that of the Marattia salicina does in New Zealand.
TheOphioglossaceæ, or Adder’s Tongue ferns, are few in number, and present comparatively little difference in structure. They are known among the exannulate series, from the Marattiaceæ, by having their fertile fronds contracted, bearing their sporangia at the margin, so that being entirely occupied by sporangia, the fertile fronds appear as if they were an inflorescence distinct from the foliaceous organs, as indeed they are analogically. In this group there is the further difference that the fronds are not circinate, but straight, in their æstivation.
These Adder’s Tongue ferns are dwarf herbaceous plants, differing greatly in structure from the true ferns, though there is some similarity to them in the fructification. They are divided into four genera, of which Ophioglossum and Botrychium are best known. The base of the stem is thick and bulbiform, and sends off spreading succulent roots. The species of the genus Ophioglossum are chiefly plants of a warm climate, but Ophioglossum vulgatum, or common Adder’s Tongue, is distributed in almost every part of the globe. In England it is exceedingly abundant in meadows and pastures, and varies in height from a few inches to a foot, in moist soil. It has one barren ovate and one fertile linear frond. The barren frond, which is of a yellowish-green colour, invests the stem of the fertile frond like a spathe; its form is ovate, varying to ovate lanceolate, and more or less obtuse, with a complicated network of anastomosing veins. Bivalved sporangia form two parallel series on the margins of the club-like terminations of the fertile frond. Soon after the fruitis shed the fronds die, but one or two buds are previously formed at the base of the plant, which remain dormant till the following spring.[74]
The genus Botrychium has few species, about half of which grow in North America. Botrychium Lunaria, or Moonwort, is the only species indigenous in Great Britain. This plant, which is from five to six inches high, has a rather long succulent stem, invested at the base by the dark-coloured membranous remains of withered leaves. It has one barren frond, the base of whose stem is a sheath, through which the tall, fertile frond rises. The barren frond has from three or four to seven pairs of opposite smooth pinnæ, of a lunate shape and glaucous green colour, overlapping each other; they are smooth, crenated on the margin, and occasionally lobed, which gives them a fan shape. The fertile frond is longer than the barren one, and ends in a panicle or thyrse. The sporangia, which are large and bivalved, are disposed in two regular series upon the divisions of the panicle, and directed towards the upper or inner face of the frond. This fructification bears a strong resemblance to that of Osmunda regalis, the Flowering fern.
The stem of this plant has been assumed to be solid and branched, which is by no means the case; for, upon dissection, it is found to be hollow, and at its base the fronds of the following year may be detected more or less perfectly formed, and the rudimentary bud of the succeeding year within the latter; the position of the barren and fertile fronds being reversed in the successive developments.