WRACK, or a name sometimes applied indiscriminately to many of the larger algce of the sea-shores, but also employed to designate the species of the genus picas (see FucAcK2E), :,ome of the most abundant ef which are employed on the British shores for the manufacture of kelp (q.v.), and are also much used as a manure. The genus fucus has a leathery, dichotomous, generally flat, linear frond, usually furnished with large air-cells, which are included in the substance of the frond; the spores arranged in tubercles, imbedded in mucus, and collected in receptacles, through the pores of wh•ch tliex are finally discharged. F. vesiculosus, popularly know as kelp.. ware, and in bcotland as black tang, is extremely abundant on all the rocky shores of Britain, growing between high and low water mark, and most plentifully near high water mark, often struggling for existence on the very upper line, and even found among grass and moss in marshy ground occasionally overflowed by the tide. It is the species chiefly employed in the kelp manufacture, because it is more easily collected than any other. It is of a dark olive-green color, sometimes 2 or 3 ft. in length; the frond flat, entire on the margin, with a central rib; the air-cells spherical, in pairs, sometimes as large as hazel-nuts; the receptacles solitary, terminal, turgid, compressed, mostly ellip tical. Oxen, sheep, and deer eat it, and seek it on the sea-shore in winter when other food is scarce. In Gothland it is boiled and mixed with a little coarse flour as food for hogs. It has been used medicinally in glandular affections, probably owing its value to the iodine which it contains.—P. nodosus is another very common British species, some
times called KNOBBED WRACK, growing nearer to low-water mark than the last, and therefore not so often and easily accessible, but esteemed the very best species for the manufacture of kelp. It has veinless fronds, branched in a somewhat pinnated man ner, with large solitary egg-shaped air-cells in the central line of the frond. It some times attains a length of 6 feet.—P. serratus is also very common, and is easily distin by its serrated fronds, and the want of air-cells. It is sometimes called BLACK RACK, It is less useful for kelp than the other species. In Norway it is used as food for cattle, generally sprinkled with a little meal. It is preferred to other species for packing crabs and lobsters to be sent to market,'as it keeps them moist, while, having less mucus than the other species, it is less apt to ferment and putrefy. Some other species of fuel's are common British duce, although much less abundant than these. The use of wrack for manure is of great advantage to farmers on the sea-coast. This kind of manure is better adapted for light than for clay soils. The effect is beneficial for almost all kinds of crop. The wrack ought not to be allowed to lie long in a heap, as it is injured by fermentation, but as quickly as possible applied to the land, and cov ered by the plow.
Some of the fuci, as F. vesiculasus and F. serrates, on receiving injury by which any part of the frond is broken, throw out a cluster of young sprouts from the injured part.