PHYSIOLOGICAL-BASIS AND ECOLOGICAL SIGNIFICANCE OF THE SEED SIZE AND RELATIVE GROWTH-RATE RELATIONSHIP IN MEDITERRANEAN ANNUALS

1. During the first three weeks of growth with plentiful water and mineral nutrients 27 Mediterranean species of annuals showed a linear negative correlation of relative growth rate (RGR) with log initial seedling weight. The lower RGR values resulted mainly from lower specific leaf area (SLA) and occurred despite higher values for unit leaf rate (ULR); they were associated with larger amounts of DNA per cell and probably with larger cell size. 2. The RGR values for a given seed size fell in the sequence Asteraceae > Poaceae > Fabaceae. The Asteraceae had the highest leaf weight ratios, the Poaceae the highest SLA values, and the Poaceae and Fabaceae the highest ULR values. 3. The result of competition between larger- and smaller-seeded species is likely to depend on the distance apart at germination. 4. The species with the largest seeds tend to occupy the soils with a richer nutrient supply and greater water-holding capacity, and thus the species which tolerate the drier, more nutrient-poor sites have smaller seeds and higher potential RGR values.