I 11 H E British marine algae of commercial importance are the red seaweeds Gigartirza stelluta and Chotdrus crispus, the littoral brown seaweed Ascophyllum nodosum, which have their habitat in the intertidal zone, and the prolific sub-littoral brown seaweeds Lamiitaria cloustoni, L. digitata and L. saccharina, which grow in large quantities attached to the rocky sea bed between low-water mark and about seven fathoms. These algae occur in greatest profusion on the more northerly rocky coasts exposed to Atlantic ocean currents such as the west coast of the Scottish mainland, the Outer and Inner Hebrides, Orkney and Shetland, although brown-seaweed beds of considerable size are also known to be located off the Welsh and Cornish coasts, the Channel Islands and in the inshore waters in the Fraserburgh and Berwickshire-Northumberland areas. Britain's seaweed resourcesA survey of the principal red-weed-bearing areas was carried out during the war (H.M.S.O., 1949) and showed that of the areas found to support harvestable amounts, the Scottish west coast was richest and supported 400 tons, of which amount 95% was G. stellata, chiefly located in the Clyde area and Skye.No quantitative survey of the brown-seaweed resources of the English and Welsh coasts has been made although a qualitative wartime assay carried out under the aegis of the Ministry of Supply (Chapman, 1948) indicated that sizable beds of both littoral and sub-littoral brown algae were located on the coasts of Wales, Cornwall, Devon, Dorset, Durham and Northumberland.Detailed quantitative surveys of the Scottish littoral brown seaweeds have been made by the Institute of Seaweed Research (Walker, rg47), who found that of the 4500 miles of Scottish coast only 540 miles supports this type of seaweed at a density of 100 tons or more per mile of coast. The total found growing at this density was I8o,ooo tons (mainly Ascophyllum nodosum), 70% of which is in the Outer Hebrides, 22% in Orkney and only 4% each in the Inner Hebrides and mainland west coast. The most prolific area found was in North Uist, where Loch Naddy and Loch Eport support a total of about 60,000 tons of littoral weed.The quantitative survey of the Scottish sub-littoral brown-seaweed beds is about one-third complete and of the seaweed so far examined in detail about 90% is one species, Laminaria cloustoizi (Scottish Seaweed Research Association, 1950). The principal sub-littoral-seaweed bearing areas so far located are Orkney, I,ZOO,OOO tons ; Outer Hebrides 700,000 tons ; Shetland 600,ooo tons ; 'riree 250,000 tons ; Kintyre and Gigha 200,000 tons, and Arran 200,ooo tons. It is reasonably certain that there are about IO,OOO,OOO tons of this type of seaweed growing between low-water mark and seven fathoms in Scottish inshore waters, of which probably not more than 4oO,<, will be easy or profitable to harvest. Composition of the brown seaweedsAlthough most of the major constituents of the Phaeophyceae were identified about 70 years ago, it was not until cliiitc recently that reliable methods for th...