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Seaweed

Collier's New Encyclopedia (1921)

a plant growing wholly in water, fresh or salt. Some are so small and delicate that they can be seen only such 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 several 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 crumpled threa 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 floating 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 grottoes and galleries. Many are larger than any trees on land, and as they are manycolored they are probably far more beautiful 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 (sargassum) 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 manure. 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 Chinese and Japanese, the Icelande 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 isinglass 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 sæ, the sea, and weod, weed.

What Has Changed in the Last Century

When Collier's wrote this in 1921, seaweeds were all filed together as "the lowest class of flowerless plants." They are no longer treated as a single group at all: green algae are close kin to land plants, red algae are a separate ancient lineage, and the brown seaweeds, including the kelps, are not classed as plants at all but as stramenopiles, related to diatoms. Two details have also been corrected: the red seaweeds are the ones that reach the greatest depths rather than being confined to the shallows, and the edible birds' nests of Chinese cookery are built from the hardened saliva of swifts, not from gelatinous seaweed. The uses the entry lists have since become a large industry, with carrageenan, agar and alginates extracted at commercial scale and tens of millions of tonnes of seaweed farmed each year, chiefly in China, Indonesia and Korea.

Written for this edition, 2026.