Sea-Weeds, Shells and Fossils

Part 1

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SEA-WEEDS, SHELLS AND FOSSILS.

PETER GRAY, A.B.S. EDIN.;

AND

B. B. WOODWARD,

Of the British Museum (Natural History), South Kensington.

LONDON: SWAN SONNENSCHEIN, LE BAS & LOWREY, PATERNOSTER SQUARE.

BUTLER & TANNER, THE SELWOOD PRINTING WORKS FROME, AND LONDON.

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 shores 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 quantity, the surface of the sea is rendered impassable 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 quantity of butter 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 Japan. 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.

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 constitute 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 Japan 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 shells of Diatoms. On various parts of our coast, the coarser 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 L30,000 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 masses of slime or jelly, others are silky to the feel, horny, 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 sexual 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 sexual process.

Following the classification 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 grass-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 mass, 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.)

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.)

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