The Melanospermav include the following orders : — Tomcat', Sporochnacece, Laminariecece, Dictyotacae, Chordariacece, Ectocar pacar.
The Tucacar, which have for their type the genus Focus, are all of them marine plants. They are of an olive brown or greenish colour, and very fine in their texture. The cellular structure of which all the Alga; are composed is in these plants in a very condensed state, assuming a leathery and sometimes even a woody character. The base of their stem or stipes forms a dense shield-like root, whilst their upper part is often expanded into a broad foliaceous appendage. The reproductive organs consist of small black or very dark spores, which are collected into sori or are found scattered on various parts of the frond. These spores are enveloped in a thick gelatinous mucus, which seems to be a provision for the purpose of attaching them more securely to the rocks on which they grow in the midst of the restless element to which they are constantly exposed. They are of very rapid growth, and only a few months serve to cover a surface of naked rock with a forest of various species of Fuci. Kelp is manu factured from the species of plants belonging to this section of Alyce; the one most commonly collected for this purpose is the Tooth resiculosua. Kelp is not now manufactured to any great extent in this country, but a few years since it was a source of great wealth in the Western Islands and the western shores of Scotland. [KELP.] At one time the quantity made in Scotland and its adjacent isles was not leas than 20,000 tons annually, which sold at the average price of 10/. per ton.
Of all the species, that which is the most common is the Fume vesiculosua, great quantities of which are cast upon our coasts, and which is known by its strap shaped, olive-green, forked divi sions, having little yellowish oval uneven pods at their points, and by the crackling noise it makes when trodden upon ; a circum stance which is owing to its stems having a considerable number of air-bladders, by means of which it floats. The structure of the pods is highly curious. Externally they consist of a hard rind, covered with tumours, each of which has a little hole in its centre. Internally they contain a soft mucous sub stance, in which lie, next the rind and immediately below its tumours, a number of round balls (a).
These little balls are composed of jointed threads (b) which hold together a great many little oval grains (c) enveloped in a sort of jelly. These grains are the spores by means of which the plant is propagated, and when ripe they are discharged through the holes in the tumours above described.
Although, from the simple structure of the Alyce, we should not expect that they would elaborate many of those secretions which in higher plants are found subservient to the use of man and other animals as food, yet among many of these a gelatinous matter is secreted, which is nutritious. In Gothland, the F. vesiculosus is given as provender to hogs, and hence is called Swine-Tang. Many other animals will also eat this plant as food, in times of scarcity. It is also collected in Jersey, and when dried is used as fuel. The fishermen both of our own and the Dutch coasts use this Fuca; and the F. serratus for pack ing up their fish ; the latter is however preferred, as, from containing less mucus, it is less likely to ferment. The Fuci were at one time used coimiderably in medicine, as well as other forme of Alyce, but since the discovery of their active principle, iodine [IODINE, ENG CYC., Ants AND Sc. Div.], they have been comparatively little used. Accord ing to Ecklon, the Laminaria buccinalia of the Cape of Good Hope is the sea-weed that producers the greatest quantity of iodine.
The Sargassum rulgare, or Tropic Grape, the Focus natans of older writers, is remarkable for the immense quantities in which it occurs in certain portions of the ocean. It only grows within forty degrees of the equator, on each side, although occasionally thrown up by currents on our own shores. In some parts of the ocean it is eo constant that it is said to assist pilots in rectifying their longitude. It was the occurrence of immense fields of these weeds that struck the sailors of Columbus with so touch awe, and led them to suppose that Providence had determined to frustrate their course, which nearly terminated in the giving up of their great attempt to discover the New World.