The New Zealand Species of Gigartina. By Bobt. M. Laing, B.Sc., F.N.Z. Inst., And H. W. Gourlay, M.Sc. Part 1. [Read before the Philosophical Institute of Canterbury, December 5th, 1928, received by Editor, December 20th, 1928; issued separately, 31st May, 1929.] Introductory. (1.) Commercial. The family Gigartinaceae includes a number of genera of which perhaps ten are to be found on the coasts of New Zealand. Of these the most abundant, both in the number of species and in quantity, is Gigartina. Immense masses of members of this genus frequently fringe the rocks on more or less exposed coasts about low-water mark. Elsewhere many species of the family have been found to have some economic value; but so far little use of them has been made commercially in New Zealand. Thus carageen (Irish Moss), a favourite remedy for colds, is prepared in quantity from Chondrus crispus and Gigartina mamillosa; and though we have neither of these species in New Zealand, yet we have others so closely allied to them, that no doubt they could be similarly employed. Indeed they have frequently been so employed locally, but so far do not appear to have entered the commercial world. Carageen could doubtless be made from Gigartina protea, G. angulata, G. clavifera and similar species. Species of the genus are elsewhere used for the manufacture of size, as a food, for jellies (used in making lollies, etc.) and in other ways. No doubt if economic conditions warranted, they could be similarly used in New Zealand. Their value consists in the amount of gelatine (gelose) which they contain. This is readily obtained by washing and boiling the plants in water, when a translucent mass, solid when cold, is obtained. This has remarkable thickening properties, and is used as a stiffener for imitation silks, muslins, nainsook, etc. There is little doubt also that agar-agar used as a culture for bacteria could be prepared from species of Gigartina, though at present chiefly obtained in India and the far east from species of Gracilaria and Gelidium. However, the algal harvests procurable from our sea coasts have yet to be recognised. General. The family as at present constituted is due to F. Schmitz and P. Hauptfleisch (1897), p. 352, but the genus Gigartina was first proposed by Lamouroux (1813) Ess., p. 48, As defined by him it contained plants now widely separated. Some species of Chordaria were