Only one species, Macrocvatls integrifolia Bory, is present in British Columbia coastal waters. It is found distributed along the whole coast in regions approaching open ocean conditions, but protected against the full ocean force, where the seawater has a specific gravity of over 1.018 at 15 degrees Centigrade and where a suitable rocky bottom, between three feet above to twenty feet below zero tide level, is available. The method of growth of the sporophyte, which is partly dichotomous and partly unilateral, is fully described from the time it is first discernible to the naked eye up to maturity. Dichotomous and subdichotomous divisions of the basal growth region are responsible for the extensive development and perennial habit of the plant. Active zoospore liberation from mature plants and young sporophytes (single, undivided blade stage) were found at least from July 1 to September but the limits were not determined. The gametophytic stages were not followed. Maximum growth (elongation) of Macrocystis recorded was 3.10" per day for a period of 29 days at the north-east of Vancouver Island. No regeneration from the holdfast or at the cut surfaces of stipes were shown as a result of cutting. Stipes of Macro cystis may continue to grow after being severed from their holdfasts. Plants removed to deeper water are retarded in rate of growth. Various practical aspects of this economically important plant are considered. It is believed two harvests per year are possible if proper precautions are taken with respect to the relative position of the terminal laminae of the plants when harvesting. A method of estimating quantities using the diameter of the stipe as an index is suggested. / Science, Faculty of / Botany, Department of / Zoology, Department of / Graduate