A polysaccharide found in brown seaweed and occurring principally in the Laminaria spp. Linear polymer composed of β-(1→3)-linked glucose residues; may contain small amounts of β-(1→6) linkages as interresidue linkages or as branch points and 2-3% d-mannitol as end groups. Two forms of laminaran are recognized; they are referred to as soluble and insoluble laminaran: Percival, Ross, J. Chem. Soc. 1951, 720. Structure: Peat et al., ibid. 1958, 724, 729; 1960, 175; Goldstein et al., Chem. Ind. (London) 1959, 124; Annan et al., ibid. 1962, 984; Annan et al., J. Chem. Soc. 1965, 885; Maeda, Nisizawa, Carbohydr. Res. 7, 97 (1968). Structure of soluble laminaran from Eisenia bicyclis: T. Usui et al., Agric. Biol. Chem. 43, 603 (1979). NMR studies of laminaran: D. Gagnaire, Org. Magn. Reson. 11, 344 (1978); H. Friebolin et al., ibid. 12, 216 (1979). Review: W. A. P. Black, E. T. Dewar in Industrial Gums, R. L. Whistler, Ed. (Academic Press, New York, 2nd ed., 1973) pp 137-145.