The life cycle of Porphyra linearis Grev. has been completed in culture to five generations. Conchosporangia formed at 5–20 °C but release of conchospores began only at the critical temperature of 13 °C, and continued at a slower rate at 5 °C. Conchocelis, the perennating phase, was long-lived despite continuous sporulation and attrition. Leafy thalli sporulated readily but seldom exceeded 4–5 cm in length. β-Spores always formed before α-spores, and both types of spore frequently occurred on a single plant. Neutral spores were not observed. Variation in ability to shed conchospores indicates the existence of strains of conchocelis.