This marine alga, the Elk Kelp, occurs from Pt. Conception, Calif., southward to some poorly defined locality off the coast of Mexico. The sori from the massive sporophytes were collected bimonthly from Oct. to Apr. and cultured in sterilized seawater with additional salts. These cultures were maintained at reduced temps. and light intensities. The results show that the optimum temp. range for gametophyte development is 8[degree] to 12[degree] C. The average maximum light intensity was 173.7 foot candles. The microscopic gametophytes are dioecious. The apical cell of the monostromatic young sporophyte divides by a longitudinal septum and this division is followed rapidly by division in the same plane by the other cells of the filament, with the exception of the basal cell which begins to elongate and forms rhizoids within 140 days.