Growth and Dormancy inLunularia cruciata(L.) Dum.: II. THE RESPONSE TO DAYLENGTH AND TEMPERATURE

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Abstract
In the Israel strain of Lunularia under investigation long-day treatment induces dormancy while short-day breaks it. Daylength is perceived by all parts of the thallus, and even by young gemmae while in the cup of the mother thallus. Since light-break treatment is equivalent to long-day the effect is truly photoperiodic, but the critical daylength is not well defined. Temperature interacts 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 the continuous light treatment preceding it. Rinsing experiments suggest that at least some of the inhibitory factor produced in long photoperiods can be leached from the plant. Dormancy-inducing treatment quantitatively confers the capacity to resist drought (dormant plants survive air-drying, while actively growing thalli are killed in 80 per cent. R.H.). The photoperiodic effects on growth and dormancy are discussed and an inhibitor hypothesis is suggested to explain the responses found.