Annual rhythm and position effect em the germemability of mesembryanthemumnodiflorum

Mesembryanthemum nodiflorum L. is an annual plant that inhabits the hottest and driest parts of Israel’s deserts. This ombrohydrochoric plant requires only extremely small amounts of rain for seed release and dispersal near the dead mother plant (topo- chory). There is no relationship between rainfall required for seed dispersal and that needed for germination. Dry closed capsules were collected in 1972 and 1974 between Jericho and the Dead Sea, and stored in the laboratory. Germination tests during the summer of 1976 and the years 1978, 1979/80, revealed an annual rhythm in seed germinability which ensures that germination is restricted to winter, the normal rainy season. Within a capsule the outer seeds are released first and have higher germination percentages than the inner seeds. This position effect (heteroblasty), together with the topochory and annual rhythm, are related to the life cycle of this plant in its desert habitat.