The life history of Grimmia pulvinata (Hedw.) SM. and Tetraphis pellucida Hedw. in the laboratory and in the field

Abstract

[2 volumes] An improved understanding of the life histories of G. pulvinata and T. pellucida was sought because both had proved to be apogamous when grown from seta cuttings. Leafy buds have not been reported in cultures of Grimmia species by previous workers. In the present study, leafy buds developed after prolonged growth of axenic protonemal cultures of G. pulvinata in daylight from the north sky but not in fluorescent light. Bud formation was not dependent on the inclusion of calcium or of EDTA in the medium. T. pellucida usually reproduces asexually by gemmae produced in a terminal cup formed by specialised leaves. Sex organs have not been reported in culture by previous workers. In the present study antheridia formed in axenic cultures where either light intensity or the concentration of mineral nutrients had been reduced. Leaf number was increased and leaf size reduced with reductions in light intensity. Protonemal cell length increased with reductions in light intensity although internode lengths of leafy shoots were not affected. Quantitative studies of cultures from single gemmae grown under coloured filters suggested a complex interaction of photosystems in the protonema. Study of shoots grown on agar with added glucose or mannitol suggested that symptoms of etiolation in the leafy shoot were not simply due to reductions in photosynthate. Gemmate shoots showed similar symptoms of etiolation both in daylight from the north sky and in light which had passed through the woodland canopy. Reduction in the size of the gemma cup leaves may aid dispersal of gemmae in shaded situations in the field. Secondary gemmate shoots were formed from basal buds on a primary gemmate shoot. In both the field and the laboratory, secondary shoots had higher leaf numbers and shorter internodes than their primary parents. Laboratory and field studies suggested that this was an effect of temperature. In shaded cultures, sex organs formed on secondary shoots with high leaf numbers in the second autumn after planting. Similarly, in the field, sex organs were found on secondary shoots with high leaf numbers; they occurred in mature turfs and their distribution was influenced by light intensity. The rarity of sexual shoots of T. pellucida in Britain may be explained by the paucity of habitats suitable for the formation and survival of a mature turf. Restriction of sex organs to secondary shoots would tend to ensure that the long process of sexual reproduction does not begin until the moss is well established in the habitat.