THE ECOLOGICAL IMPORTANCE OF SEED DIMORPHISM IN CORN SPURRY (SPERGULA ARVENSIS L.) I: THE EFFECTS OF DAY LENGTH ON SEED GERMINABILITY

Spergula arvensis L. is a heteromorphic species of the Caryophylla- ceae family, that produces two types of seeds with a smooth or papillate (P) coat. The plant flowers and produces fruit between May and September, a period marked by a gradual decrease in day length. The objective of this study was to determine the effects of day length on the germinabiity of heteromorphic seeds. In addition, we examined the frequencies of non papillate and papillate seeds in four populations. Germination tests were performed on seeds harvested from plants grown in a greenhouse under conditions simulating long days and short days. Heteromorphic seeds incubated in water at various temperatures over a period of 4 weeks remained dormant. The majority of individuals were monomorphic and produced capsules containing only one type of seed. Heteromorphic individuals produced capsules containing: a) NP seeds, and b) P seeds, and c) mixed seeds. The analyzed populations were characterized by a predominance of P seeds in the overall seed pool.