AbstractAn experimental study of growth and reproduction inPleurozium schreberiwas undertaken to obtain information on the species seasonal pattern of growth and the previously reported irregular distribution of perigonia and sporophytes in the field in Great Britain. Humid conditions and the regular application of water and mineral nutrients in solution directly to the leafy shoots were found necessary for the sustained growth of mature gametophores. Under these conditions the rate of growth increased with increase in temperature independently of photoperiod over the range 5–20°C. No consistent differences in growth rate between male and felnale plants were recorded.Most tetrads in immediately post-meiotic capsules were shown to contain at least three and often four developing spores. Mature capsules contained normal and aborted spores, the frequency of the latter normally being 0–40%. Over 95% germination of normal spores was consistently achieved on agar. The rate of germination increased with temperature, day-length having only a slight effect. Regeneration by detached leaves occurred only in the case of young leaves, particularly those from close to the stem apex and on the uppermost branches where the stem and branch axes remained green in colour. Over 80% of such leaves normally gave rise to secondary protonemal filaments, which arose from enlarged cells in the basal angles, and many subsequently produced leafy buds. Bud formation was more frequent in male leaves (58%) than females (28%) on moist filter paper but little difference between males and females was recorded on peat-sand mixture.The explanation of a predominance of female plants in most British populations remains obscure but it is suggested that it may have its origin in events between meiosis and the protonemal stage.