Growth and Dormancy in Lunularia cruciata (L.) Dum.: I. RESUMPTION OF GROWTH AND ITS CONTINUATION

Lunularia cruciata may become dormant at three stages in itslife history: mature thallus, gemma, and spore. The resumptionof growth and its continuation in various conditions have beenstudied in thalli and gemmae. Air-dry, mature thalli of theIsrael strain, planted on a suitable medium, produce adventitiousbranches ventrally from the region immediately posterior tothe existing meristem, which itself fails to resume growth.When dormant gemmae are taken from the gemma-cup, however, theexisting apical cells and meristems simply recommence growing,so that the new growth is continuous with the old. Except inthe case of mature thalli aroused from dormancy, apical dominanceis pronounced, and branching occurs only by bifurcation. Thisdominance can be broken by applying sucrose solution to thegrowing tips—possibly a plasmolytic effect. The growth in area of freshly planted gemmae accelerates forabout 25 days before its relative rate slows to any great extent.During the first half of this period, growth is due exclusivelyto the expansion of existing cells, but subsequently cell numbersincrease rapidly from the 8–10,000 present in the dormantgemma. Cell numbers were estimated by using a modified macerationtechnique, in which chelation followed prolonged fixation. Lunularia grows successfully at quite low light intensities.Of the mineral nutrient deficienccs investigated, lack of Plimits growth most severely, although N-deficiency also restrictsit to a very low level. Gemma-cup production appears to be unaffected by light intensity,at least within levels permitting growth. There is, however,a large temperature effect, cup production decreasing markedlyabove 12° C.     

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

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.