Sea-Weeds, Sh.e.l.ls and Fossils.

by Peter Gray and B. B. Woodward.

SEA-WEEDS.

BY PETER GRAY.

Algae, popularly known as sea-weeds, although many species are inhabitants of fresh water, or grow on moist ground, may be briefly described as cellular, flowerless plants, having no proper roots, but imbibing nutriment by their whole surface from the medium in which they grow. As far as has been ascertained, the total number of species is about 9000 or 10,000. Many of them are microscopic, as the Desmids and Diatoms, others, as Lessonia, and some of the larger Laminariae (oarweeds), are arborescent, covering the bed of the sea around the coast with a submarine forest; while in the Pacific, off the northwestern sh.o.r.es of America, Nereocystis, a genus allied to Laminaria, has a stem over 300 feet in length, which, although not thicker than whipcord, is stout enough to moor a bladder, barrel-shaped, six or seven feet long, and crowned with a tuft of fifty leaves or more, each from thirty to forty feet in length. This vegetable buoy is a favourite resting place of the sea otter; and where the plant exists in any quant.i.ty, the surface of the sea is rendered impa.s.sable to boats. The stem of Macrocystis, which "girds the globe in the southern temperate zone," is stated to extend sometimes to the enormous length of 1500 feet. It is no thicker than the finger anywhere, and the upper branches are as slender as pack-thread; but at the base of each leaf there is placed a buoy, in the shape of a vesicle filled with air.

Although the worthlessness of Algae has been proverbial, as in the "alga inutile" of Horace and Virgil's "projecta vilior alga," they are not without importance in botanical economics. A dozen or more species found in the British seas are made use of, raw or prepared in several ways, as food for man. Of these edible Algae, Dr. Harvey considers the two species of Porphyra, or laver, the most valuable. Berkeley says, "The best way of preparing this vegetable or condiment, which is extremely wholesome, is to heat it thoroughly with a little strong gravy or broth, adding, before it is served on toast, a small quant.i.ty of b.u.t.ter and lemon juice." A species of Nostoc is largely consumed in China as an ingredient in soup. A similar use is made of Enteromorpha intestinalis in j.a.pan. Many species of fish and other animals, turtle included, live upon sea-weed. Fucus vesiculosus is a grateful food for cattle. In Norway, cattle, horses, sheep, and pigs are largely fed upon it, and on our own coasts cattle eagerly browse on that and kindred species at low water. In some northern countries, Fucus serratus sprinkled with meal is used as winter fodder.

[Ill.u.s.tration: Fig. 1. Group of Sea-weeds (chiefly Laminariae)]

All the marine Algae contain iodine; and even before the value of that substance in glandular complaints had been ascertained, stems of a sea-weed were chewed as a remedy by the inhabitants of certain districts of South America where goitre is prevalent. Chondrus crispus and (Gigartina) mamillosa const.i.tute the Irish moss of commerce, which dissolves into a nutritious and delicate jelly, and the restorative value of which in consumption doubtless depends in some degree on the presence of iodine. The freshwater Algae not only furnish abundant and nourishing food to the fish and other animals living in ponds and streams, but by their action in the decomposition of carburetted hydrogen and other noxious gases purify the element in which they live, thus becoming important sanitary agents. The value of aquatic plants in the aquarium is well known. A Chinese species of Gigartina is much employed as a glue and varnish; and also much used in China in the manufacture of lanterns and transparencies, and in that country and j.a.pan for glazing windows. Handles for table knives and forks, tools, and other implements have been made from the thick stems of oarweeds, and fishing lines from Chorda filum. Tripoli powder, extensively used for polishing, consists mainly of the silicious sh.e.l.ls of Diatoms. On various parts of our coast, the coa.r.s.er species of sea-weed, now used as a valuable manure, were formerly extensively burnt for kelp, an impure carbonate of soda. This industry, when carried on upon a large scale, became a fruitful source of income to some of the poorest districts in the kingdom, bringing, in the last decade of last century, nearly 30,000 per annum into Orkney alone.

Since the production of soda from rock salt has become general, kelp is now only burnt for the extraction of iodine, this being the easiest way of obtaining that substance.

Although the vegetable structure and mode of reproduction are essentially the same in all Algae, as regards the former they vary from the simple cell, through cells arranged in threads, to a stem and leaves simulating the vegetation of higher tribes. And although the simpler kinds are obviously formed of threads, most of the more compound may also be resolved into the same structure by maceration in hot water or diluted muriatic acid. In substance some are mere ma.s.ses of slime or jelly, others are silky to the feel, h.o.r.n.y, cartilaginous or leather-like, and even apparently woody. A few species secrete carbonate of lime from the water, laying it up in their tissues; others cover themselves completely with that mineral, while some coat themselves with silex or flint. Many Algae are beautifully coloured, even when growing at depths to which very little light penetrates. As in their vegetative organs, so in their reproductive, Algae exhibit many modifications of structure without much real difference. In the green sea-weeds reproduction is effected by simple cell division in the unicellular species, and by spores resulting from the union of the contents of two cells in the others. The red sea-weeds have a double system of reproduction, a distinctly s.e.xual one, by spores and antheridia, and another by tetraspores, which by some are considered to be of the nature of gemmae, or buds. The spores are generally situated in distinct hollow conceptacles (favellae, ceramidium, coccidium). The tetraspore is also sometimes contained in a conceptacle. It consists of a more or less globular, transparent cell, which when mature contains within it four (rarely three) sporules.

Reproduction in the olive sea-weeds is also double, by zoospores, generally considered gemmae, and by spores and antherozoids, which is a s.e.xual process.

[Ill.u.s.tration: Fig. 2. A, Species of Gleocapsa, one of the Palmelleae, in various stages. A becomes B, C, D, and E by repeated division. Magnified 300 diameters.]

Following the cla.s.sification adopted by Professor Harvey, which is that generally employed in English systematic manuals, we divide the order into three sub-orders, named from the prevailing colour of their spores. 1. Chlorospermeae, with green spores; 2. Rhodospermeae, with red spores; and 3. Melanospermeae, with olive-coloured spores. The entire plant in the first group is usually gra.s.s-green, but occasionally olive, purple, blue, and sometimes almost black; in the second it is some shade or other of red, very seldom green; and in the third, while generally olive green, it is occasionally brown olive or yellow.

The Chlorospermeae are extremely varied in form, often threadlike, and are propagated either by the simple division of the contents of their cells (endochrome), by the transformation of particular joints, or by the change of the contents of the cells into zoospores, which are cells moving freely in water by means of hairlike appendages. In their lower forms they are among the most rudimentary of all plants, and thus of special interest physiologically, as representing the component parts of which higher plants are formed. They are subdivided into twelve groups, as follows:

The first group, Palmelleae, are unicellular plants, the cells of which are either free or surrounded by a gelatinous ma.s.s, and they are propagated by the division of the endochrome. One of the most remarkable of the species of this family is Protococcus cruentus, which is found at the foot of walls having a northern aspect, looking as if blood had been poured out on the ground or on stones.

Protococcus nivalis, again, is the cause of the red snow, of which early arctic navigators used to give such marvellous accounts.

(Fig. 2.)

[Ill.u.s.tration: Fig. 3. A, Fragment of a Filament of Zygnema, one of the Conjugateae; B, Closterium; C, Euastrium; two desmids.]

The Desmideaceae, together with the plants of the next succeeding group, are favourite subjects of investigation or observation by the possessors of microscopes, an attention they merit from the beauty and variety of their forms. They are minute plants of a green colour, consisting of cells generally independent of each other, but sometimes forming brittle threads or minute fronds, and are reproduced by spores generated by the conjugation of two distinct individuals. The process of conjugation in Desmids and Diatoms consists in the union of the endochrome of two individuals, each of which in these families is composed of a single cell. This ultimately forms a rounded body or resting spore, which afterwards germinates, the resulting plant not however acquiring the normal form until the third generation. (Fig.

3.)

The Diatomaceae, closely allied to the preceding group in structure and reproduction, are however distinguished from them by their flinty sh.e.l.ls, which are often beautifully sculptured. Their endochrome is a golden brown, instead of green as in the Desmideaceae. The latter, also, are confined to fresh water, while the Diatomaceae are found, though not exclusively, in the sea, where their sh.e.l.ls sometimes, microscopically minute as they are individually, form banks extending several hundred miles. It is stated that in the collection made by Sir Joseph Hooker in the Himalayas the species closely resemble our own.

In the next group, Confervaceae, we are introduced to forms more like the general notion of what a plant should be. The individuals of which it consists are composed of threads, jointed, either simple or branched, mostly of a gra.s.s-green colour, and propagating either by minute zoospores or by metamorphosed joints. They are found both in fresh and salt water, and in damp situations. The number of species is very great. A considerable number consist of unbranched threads; the branched forms grow sometimes so densely as to a.s.sume the form of solid b.a.l.l.s. After floods, when the water stands for several days, they sometimes increase to such an extent, as to form on its subsidence a uniform paper-like stratum, which while decomposing is extremely disagreeable. The name Conferva has been almost discontinued as a generic t.i.tle, the majority of British species being now ranged under Clado- and Chaeto-phora. The latter are branched, and require great care and attention in order to distinguish them, on account of their general resemblance to each other. Good characters are however to be found in their mode of branching and the form and comparative size of the terminal joints.

The Batrachospermeae const.i.tute a small but very beautiful group, consisting of gelatinous threads variously woven into a branched cylindrical frond. The branches are sometimes arranged, as in the British species, so that the plants appear like necklaces. In colour they pa.s.s from green, through intermediate shades of olive and purple, to black. In common with some of the higher Algae, the threads of the superficial branches send joints down the stem, changing it from simple to compound. The native species are all fluviatile.

The Hydrodicteae are among the most remarkable of Algae. Hydrodictyon utriculatum, the solitary British species, is found in the large pond at Hampton Court, and in similar situations in various parts of the country, but not very generally. It resembles a green purse or net, from four to six inches in length, with delicate and regular meshes, the reticulations being about four lines long. Its method of reproduction is no less than its form. Each of the cells forms within itself an enormous ma.s.s of small elliptic grains. These become attached by the extremities so as to form a network inside the cell, and, its walls being dissolved, a new plant is set free to grow to the size of the parent Hydrodictyon.

The Nostochineae grow in fresh water, or attached to moist soil. They consist of slender, beaded threads surrounded by a firm jelly, and often spreading into large, wavy fronds. The larger beads on the inclosed threads are reproductive spores. (Fig. 4, A.)

[Ill.u.s.tration: Fig. 4. A, Fragment of a Filament of Nostoc. B, End of a Filament of Oscillatoria.]

The Oscillatoreae are another remarkable group, on account of the peculiar animal-like motions they exhibit. They occur both in salt and fresh water, and on almost every kind of site in which there is sufficient moisture. The threads of which they are composed are jointed, and generally unbranched; they are of various tints of blue, red, and green, and, where their fructification has been ascertained, are propagated by cell division. The most curious point about them is, however, the movements of their fronds. According to Dr. Harvey, these are of three kinds--a pendulum-like movement from side to side, performed by one end, whilst the other remains fixed, so as to form a pivot; a movement of flexure of the filament itself, the oscillating extremity bending over from one side to the other, like the head of a worm or caterpillar seeking something on its line of march; and lastly, a simple onward movement of progression, the whole phenomenon being, Dr. Harvey thinks, resolvable into a spiral onward movement of the filament. Whatever is the cause of this motion, it is not, as used to be supposed, of an animal nature; for the individuals of this group are undoubted plants. (Fig. 4, B.) Several species of Rivularia, belonging to the Oscillatoreae, are found both in the sea and in fresh water. They are gelatinous, and have something of the appearance of Nostoc, in aspect as well as in minute structure.

The Conjugatae are freshwater articulated Algae, which reproduce themselves by the union of two endochromes. They are very interesting objects under the microscope, owing to the spiral or zigzag arrangement of the endochrome of many of them, and the delicacy of all.

The Bulbochaeteae const.i.tute a small group, some half-a-dozen species being British. They are freshwater plants, composed of articulate branched filaments, with fertile bulbshaped branchlets. The endochrome is believed to be fertilized by bodies developed in antheridia, the contents of each fertilized cell dividing into four ovate zoospores.

The last two groups of green sea-weeds consist chiefly of marine plants. Of these the first, Siphoneae, is so called because the plant, however complicated, is composed invariably of a single cell. It propagates by minute zoospores, by large quiescent spores, or by large active spores clothed with cilia. It includes the remarkable genus Codium, three species of which inhabit the British seas. In Codium Bursa the filamentous frond is spherical and hollow, presenting more the appearance of a round sponge or puff-ball than a sea-weed, and is somewhat rare. Another species greatly resembles a branched sponge, and the third forms a velvety crust on the surface of rocks. Another genus, Vaucheria, is of a beautiful green colour, forming a velvety surface on moist soil, on mud-covered rocks overflowed by the tide, or parasitic on other sea-weeds. The most attractive plants of this family are however those of the genus Bryopsis, two of which are found on the British sh.o.r.es. The most common one is B. plumosa, the fronds of which grow usually in the shady and sheltered sides of rock pools.

The fronds of the last of the green-weed groups, the Ulvaceae, are membranous, and either flat or tubular. Two of them, Ulva latissima, the green, and Porphyra laciniata, the purple laver, are among the most common sea-weeds, growing well up from low-water mark. The propagation in all of them is by zoospores. An allied genus, Enteromorpha, is protean in its forms, which have been cla.s.sed under many species. They may, however, be reduced to half a dozen. Some of them are very slender, so as almost to be mistaken for confervoid plants.

With the Rhodospermeae we enter a sub-order of Algae, exclusively marine, the plants in which have always held out great attractions to the collector. In structure they are expanded or filamentous, nearly always rose-coloured or purple in colour. Of the fourteen groups into which they are divided by Harvey, the first is Ceramiaceae, articulate Algae, const.i.tuting a large proportion of the marine plants of our sh.o.r.es. Of the genus Ceramium, C. rubrum is the most frequent, and it is found in every lat.i.tude, almost from pole to pole. It is very variable in aspect, but can always be recognized by its fruit. C.

diaphanum is a very handsome species, growing often in rock pools along with the other. There are about fifteen native species altogether, some of them rare, and all very beautiful, both as displayed on paper and seen under the microscope. Crouania attenuata is a beautiful plant, parasitic upon a Cladostephus or Corallina officinalis. It is however extremely rare, being only found in England about Land's End. A more common and conspicuous, but equally handsome plant is Ptilota plumosa (Fig. 9), which is mostly confined to our northern coasts; although P. sericea, a smaller species, or variety, is common in the south, and easily distinguished from its congener, which it otherwise greatly resembles, by its jointed branchlets and pinnules. Callithamnion, Halurus and Griffithsia, articulate like Ceramium, furnish also several handsome species. (Fig. 5.)

[Ill.u.s.tration: Fig. 5. Species of Callithamnion.]

The group Spyridiaceae contains only one English plant, Spyridia filamentosa, which is curiously and irregularly branched, the branches being articulate and of a pinky red. One of its kinds of fruit, consisting of crimson spores, is contained in a transparent network basket, formed by the favellae, or short branches, whence its name.

[Ill.u.s.tration: Fig. 6. Chondrus crispus.]

The Cryptonemiaceae are very numerous in genera and species. They all have inarticulate branches, some are thread-like. Grateloupia filicina is a neat little plant, met with rarely on the south and west coasts.

Gigartina mamillosa, a common plant everywhere, is the plant sold, along with Chondrus crispus, as Irish or Carrageen moss. A handsome little plant, Stenogramme interrupta, is very rare, but it has been gathered both on the Irish and English coasts. The Phyllophorae, one species of which is frequent on all our sh.o.r.es, may be recognised by the way in which the points and surfaces of their fronds throw out proliferous leaves. Gymnogongrus has two British species, one much resembling Chondrus crispus, already named, of which it was formerly considered a congener. Their fructification is however very different.

Ahnfeltia plicata is a curiouswiry, entangled plant, almost black in colour, and like horse-hair when dry, and can scarcely be mistaken.

Cystoclonium purpurascens is very commonly cast up by the tide on most of our coasts. It varies in colour, but is easily distinguished by the spore-bearing tubercles imbedded in its slender branches. Callophyllis laciniata is a handsome species, of a rich crimson colour, and sometimes a foot square. It can scarcely have escaped the notice of the sea-side visitor, for it is widely distributed and often thrown out in great abundance; one writer describes the sh.o.r.e near Tynemouth as having been red for upwards of a mile with this superb sea-weed.

Kalymenia reniformis is another of the broad, flat Algae, but it is scarcer, and of a colour not so conspicuous. Among the most frequent of our sea-weeds, both as growing in the rock pools and cast ash.o.r.e, is Chondrus crispus, already twice referred to in connexion with its officinal uses. It is very variable in form, one author figuring as many as thirty-six different varieties. (Fig. 6.) Chylocladia clavellosa, which is sometimes cast ash.o.r.e a foot and a half long, is closely set with branches, and these again clothed with branchlets in one or two series. The whole plant is fleshy, of a rose-red or brilliant pink colour, turning to golden yellow in decay. There is another small species, confined to the extreme north of Britain.

Halymenia ligulata is another flat red weed, but sometimes very narrow in its ramifications. Furcellaria fastigiata has a round, branched, taper stem, swollen at the summit, which contains the fruit, consisting of ma.s.ses of tetraspores in a pod-like receptacle.

Schizymenia edulis, better known perhaps by its old name Iridea, is a flat, inversely egg-shaped leaf with scarcely any stem. It is one of the edible Algae, and pretty frequent in shady rock pools.

Gloiosiphonia capillaris is a remarkably beautiful plant, and not common, being confined to certain parts of the southern coasts. The stem is very soft and gelatinous; the spores are produced in red globular ma.s.ses imbedded in the marginal filaments, which have a fine appearance under the microscope when fresh.

[Ill.u.s.tration: Fig. 7. Rhodomenia palmata.]

[Ill.u.s.tration: Fig. 8. Wormskioldia sanguinea.]

The Rhodomeniaceae are purplish or blood-red sea-weeds, inarticulate, membranaceous, and cellular. Among the dark-coloured is Rhodomenia palmata, better known as dulse, a common and edible species. (Fig. 7.) Wormskioldia sanguinea is not only the most beautiful sea-weed, but the finest of all leaves or fronds. It is usually about six inches long, but sometimes nearly double that length and six inches broad, with a distinct midrib and branching veins, and a delicate wavy lamina, pink or deep red. The fruit is produced in winter from small leaflets growing upon the bare midrib. (Fig. 8.) The commonest of all red sea-weeds on our coast, one of the most elegant, and much sought after by sea-weed picture makers, Plocamium coccineum, belongs to this group. Calliblepharis ciliata and jubata are coa.r.s.er plants, the latter being the more frequent. They were formerly included in the genus Rhodymenia, from which they were removed when their fruit was better understood.

[Ill.u.s.tration: Fig. 9. Ptilota plumosa.]

Wrangelia and Naccaria are the only British genera in Wrangeliaceae.

There is only one native species in each, both being rare, the latter especially.

The Helminthocladiae are also a limited group, of a gelatinous structure; so much so that on being gathered they feel like a bunch of slimy worms, whence the name of the family. Helminthora purpurea and divaricata with Nemaleon multifidum and Scinaia furcellata represent them in Britain. They are nearly all very rare, pretty plants, and very effective as microscopic objects.

The Squamariae, formerly included in the Corallinaceae, are a small group of inconspicuous plants resembling lichens, of a leathery texture, and growing on rocks and sh.e.l.ls attached by their lower surface.

A single genus only, Polyides, represents the Spongiocarpeae. Polyides rotundus resembles Furcellaria fastigiata very closely, but differs widely in the fruit, which consists of spongy warts surrounding the frond, composed of spores and articulated threads.

Of the next group represented in Britain, Gelidiaceae, we have only one plant, Gelidium corneum, very common on our sh.o.r.es, and perhaps the most variable of all vegetable species.

The Sphaerococcidae include both membranaceous and cartilaginous species. Of the latter is Sphaerococcus coronopifolius, which cannot easily be mistaken, owing to the numerous berry-like fruits that tip its branchlets. It is rather rare on the northern, but often thrown ash.o.r.e in large quant.i.ties on the southern coasts. The genus Delesseria has four British species, the largest being the well-known D. sinuosa, the fronds of which resemble an oak leaf in outline. The handsomest are D. ruscifolia and D. hypoglossum, which are more delicate and of a finer colour than sinuosa. There are three British species of Gracillaria, in two of which the branches are cylindrical, and in the other flat. G. compressa makes an excellent preserve and pickle, but unfortunately it is the rarest of the three. Nitophyllum is one of the greatest ornaments of this tribe. There are six British species, which are amongst the most delicate and beautiful of our native Algae.

The Corallinaceae are remarkable for the property they possess of absorbing carbonate of lime into their tissues, so that they appear as a succession of chalky articulations or incrustations. The most common is Corallina officinalis. There are two British species of Corallina, and two also of the nearly allied genus, Jania. Of the foliaceous group there are likewise two British genera, Melobesia and Hildenbrantia.