| Popis: |
The date-of-flowering of Ranunculus penicillatus (Dum.) Bab. var. calcareus (R.W. Butcher) C.D.K. Cook was progressively later down the length of the R. Piddle and resulted in a 2–3 month delay between the date at the source and the tidal limit. Transplants between the extremes of conditions existing in this area showed that the date remained the same as that of the collection site, for several years. The induction of flowering under the natural range of conditions in the R. Piddle area is unlikely to be a result of a change in photoperiod, or of any quantitative or critical effect of water temperature, although the rate of development of the flower buds was dependent in part on temperature. Plants subjected experimentally to different photoperiods, in an attempt to change the time of induction, continued to flower on the same date for three successive years. The plants were exposed to 8, 15 and 4-hourly alternations of dark and light, in every 24 h in growth chambers supplied with artificial ‘natural’ light. It is suggested that there is an ecocline of genetic material down this river and that the plants' growth cycle is probably adapted to optimum conditions at each site. |
