S U M M A I< YEmbryo dormancy in seeds of httpatiens glandulifera Royle can be overcome by maintaining them imbibed at 4 °C. The period of chilling required depends on the age and storage conditions of the dry seed; it decreases with seed age and is reduced by a high storage temperature. Fully imbibed seeds can remain dormant for several years at 20 °C if the stratification requirement is not met. Interrupting stratification at 4 °C with a period at 20 °C increases the chilling requirement in proportion to the length of the warm period. However interrupting stratification by desiccation has no etfect on the chilling period required. The ecological implications of these findings are discussed.Key v\'ords: Stratification, embryo dormancy, Impatietis glandulifera.In recent years the species Itnpatiens glattdulifera Royle has spread widely throughout damp areas ot natural vegetation of Britain (Clapham, Tutin & Warburg, 1981). I'he seedlings emerge in late spring and the numerous seeds are dynamically dispersed from July until October. Seed dormancy is known in many Impatiens species (Barton, 1939; Kroeger, 1941) and may be broken by a period of cold stratification; Impatiens glandulifera is no exception. This species originated in tbe Himalaya where a dormancy mechanism dependent upon abrupt seasonal temperature changes could aid the survival of the species over the severe winter period.Attempts to germinate the seeds of this species under laboratory conditions after periods of 6 weeks to 6 montbs chilling of imbibed seeds proved variable and therefore a series of experiments were undertaken to investigate its cold stratification requirements.M.'VTERIALS AND Ml'.TIIODS Seed of Impatiens glattdulifera Royle were collected from the wild in September 1983 and 1984 and were harvested from plants raised under glass in tbe summer and autumn of 1985 and 1986. Tbe seeds were air dried and sealed in metal cans and stored at 4 C until use. Germination tests were conducted on all freshly harvested seeds and fresh seeds were allowed to fully imbibe and were maintained moist at 4 °C. Periodically seeds were withdrawn from chilling to test germination ai-id those which did not germinate within 2 weeks were returned to 4 °C for a turther period. Dry stored seeds were also sampled periodically and imbibed and chilled at 4 °C until an indication ot dormancy break was observed vvben they were removed to germination conditions. Some seeds barvested in 1986 were also stored dry at temperatures of 15, 25 and 35 °C and their chilling requirements were tested. The stratification period given varied from 12 to 48 days and was selected because it caused dormancy break in seeds from at least one storage treatment.To examine tbe effect of various periods of warm imbibition before chilling on dormancy, seeds were imbibed for 2-5 days at 20 °C and tben transferred to 4 °C. At weekly intervals initially, and later at 2-weekly intervals, seeds were replaced at 20 °C for germination. Control seeds, which had been maintained dry at 4 °C for 18 ...

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SUMMARYParental lines (inbred and hybrid male‐sterile lines and inbred pollinators) of prospective F, hybrids from the NVRS spring‐sown bulb onion breeding programme were examined to study their floral biology and aspects of pollination under glasshouse conditions. Inbreeding depression occurred in both pollinator and male‐sterile inbreds in terms of reduced flower numbers per umbel and a greater proportion of defective pistils. Male‐sterile and male‐fertile lines differed in their stigma and style characteristics and pattern of development. At flower opening, the styles of male‐sterile lines were longer and the stigmatic knob became receptive relatively sooner. The inbred male‐sterile line II/3 ms appeared to have a reduced receptive area on its stigmatic knob and remained receptive for a relatively shorter period. Individual lines differed for time of flowering, nectar content and its sugar concentration, and in their effectiveness as male and female parents as judged from pollen tube growth down the style in specific pairings. Assessment of pollen viability using the fluorescein diacetate test did not correlate with assessments based on pollen grain germination and subsequent growth down the style, perhaps as a result of differential receptivity in the inbred lines tested.These results are discussed in relation to future hybrid seed production.

SUMMARYWhen dormancy is broken by chilling in Impatiens glandulifera Royle anthocyanin appears in the cells of the root cap acting as a marker of the physiological condition of the seeds. This precedes growth of the embryo as indicated by increase in seed weight. Abscisic acid at some concentrations can inhibit dormancy break and anthocyanin synthesis in the root cap. All tissues of the embryo, when excised, responded independently to the cold stimulus. Grafting pieces of dormant and non-dormant seed showed the agent effective in breaking dormancy was not transmissible between a piece of chilled embryo placed in contact with a piece of dormant embryo.