SEED SIZE VARIATION IN DESMODIUM-PANICULATUM .1. FACTORS AFFECTING SEED SIZE

(1) In a population of Desmodium paniculatum seed weight varies by a factor of about four. Increase in temperature during the growth of the plants, reduces nutrient and water availability, and shortening of the photoperiod decreases the mean seed weight. A 50% reduction (to mimic grazing loss) in total leaf area during seed development increases mean seed weight of plants grown at high temperatures. (2) Seed size varies significantly among individual plants, but there is no correlation between mean and weight per plant and total numbers of seeds produced per plant. Within a plant, seed size may vary by as much as a factor of two if grown under high-nutrient supply, but this variability is significantly reduced if plants are grown with limited nutrients. Part of the within-plant variability is due to the production of fruits with a variable number of seeds and to the position of the seed within a fruit. Seedlings from different positions within the fruit have different probabilities of survival. (3) In plants grown with low (but not with high) nutrients, parental seed sizes are positively correlated with offspring seed sizes. Seed size may thus affect the subsequent generation.