| Abstract: | In the Israel strain of Lunularia under investigation long-daytreatment induces dormancy while short-day breaks it. Daylengthis perceived by all parts of the thallus, and even by younggemmae while in the cup of the mother thallus. Since light-breaktreatment is equivalent to long-day the effect is truly photoperiodic,but the critical daylength is not well defined. Temperatureinteracts strongly with photoperiod. High temperature (24°C.) combined with continuous light rapidly induces dormancy(c. 6 days). Fewer short days are required to restart growth,and the number (3–4) is unaltered by the duration of thecontinuous light treatment preceding it. Rinsing experimentssuggest that at least some of the inhibitory factor producedin long photoperiods can be leached from the plant. Dormancy-inducingtreatment quantitatively confers the capacity to resist drought(dormant plants survive air-drying, while actively growing thalliare killed in 80 per cent. R.H.). The photoperiodic effects on growth and dormancy are discussedand an inhibitor hypothesis is suggested to explain the responsesfound. |
