SEAWEED, a plant growing wholly in water, fresh or salt. Some are so small and delicate that they can be seen only with a microscope, and others are of such immense growths that they almost fill up the seas in which they live. The great seaweeds called sea aprons are often sev eral hundred feet long. Seaweeds are not much like the plants that grow on land. They have no roots and therefore do not get any of their food from the earth, but live entirely from the water. Many float around in the water and many are fastened to rocks at the bottom of the sea, to which they are made fast by a kind of stem with a sticky surface. They have no real leaves, but have parts which answer for leaves. Sometimes these are like wavy thongs, sometimes like crumpled threads; others are like fans, balloons, belts, delicate ribbons, or shreds of jelly. Some are thick and tough, others thin and tender; and they are of many colors. Those in deep water are mostly brown, of different shades, and those nearer the surface and often float ing are mostly green; the pinks and reds are found chiefly in shallow water near the shore.
In the bottom of the ocean the seaweeds form great groves and woods which lace their branches together and make grot toes and galleries. Many are larger than any trees on land, and as they are many colored they are probably far more beau tiful than our forests. The seaweeds that float often form islands which drift about in the currents. Not far from the Azores is an immense bank of seaweed called the Sargasso Sea from the kind of weed (sar gassum) of which it is made up.
Many of the seaweeds are very useful to man. In eastern Europe they are dried for fuel and put on land for ma nure. The seaweed called bladder wrack and knobbed rack were once much used for making kelp. In northern Europe these are fed to pigs, and when food is scarce even horses and cattle thrive on them. In Holland a kind of seaweed is used in building dykes or banks to keep the sea from flowing on to the land, and the same kind is also used for stuffing mattresses and cushions and for packing goods. The Sandwich Islanders, the Chi nese and Japanese, the Icelanders, and many other people eat various kinds of seaweeds. The edible birds' nests of the Chinese are said to be built by swallows out of a kind of seaweed which has much gelatine in it. Another kind in China contains so much gelatine that it is largely used for making glue and varnish. Among the most useful of the seaweeds is that commonly called Irish moss or carrageen, which takes the place of isin glass in making blancmange and jellies, and is used also in making sizing and lager beer. Dulse, a purple seaweed, called dillesk by the Irish, is also collected and used for food.
Seaweeds belong to the lowest class of flowerless plants. They do not have seeds, but grow from spores, as do lichens.
The word seaweed is made up of the Anglo-Saxon sir, the sea, and weod, weed.