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 min eral nutrients 27 Mediterranean species of annuals showed a linear neg ative correlation of relative growth rate (RGR) with log initial seedl ing weight. The lower RGR values resulted mainly from lower specific l eaf area (SLA) and occurred despite higher values for unit leaf rate ( ULR); they were associated with larger amounts of DNA per cell and pro bably with larger cell size. 2. The RGR values for a given seed size f ell in the sequence Asteraceae > Poaceae > Fabaceae. The Asteraceae ha d 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 de pend on the distance apart at germination. 4. The species with the lar gest seeds tend to occupy the soils with a richer nutrient supply and greater water-holding capacity, and thus the species which tolerate th e drier, more nutrient-poor sites have smaller seeds and higher potent ial RGR values.