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

Abstract

Lunularia cruciata may become dormant at three stages in its life history: mature thallus, gemma, and spore. The resumption of growth and its continuation in various conditions have been studied in thalli and gemmae. Air-dry, mature thalli of the Israel strain, planted on a suitable medium, produce adventitious branches ventrally from the region immediately posterior to the existing meristem, which itself fails to resume growth. When dormant gemmae are taken from the gemma-cup, however, the existing apical cells and meristems simply recommence growing, so that the new growth is continuous with the old. Except in the case of mature thalli aroused from dormancy, apical dominance is pronounced, and branching occurs only by bifurcation. This dominance can be broken by applying sucrose solution to the growing tips—possibly a plasmolytic effect. The growth in area of freshly planted gemmae accelerates for about 25 days before its relative rate slows to any great extent. During the first half of this period, growth is due exclusively to the expansion of existing cells, but subsequently cell numbers increase rapidly from the 8–10,000 present in the dormant gemma. Cell numbers were estimated by using a modified maceration technique, in which chelation followed prolonged fixation. Lunularia grows successfully at quite low light intensities. Of the mineral nutrient deficienccs investigated, lack of P limits growth most severely, although N-deficiency also restricts it 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 markedly above 12° C.