Seeds as allelopathic agents.

Inhibitors of germination or of growth, highly diversified chemicals are commonly found in higher plants. They occur in vegetative organs as well as in seeds or other dispersal units. Nonprotein amino acids, when present, are mainly found in seeds where they can occur in extremely high concentrations. Density of seeds, rate of emanation of inhibitors, their amount and effectiveness, all determine allelopathic potential of seeds. To induce allelopathy, rate of emanation of inhibitors must be fast and of sufficient duration. Our observations in coffee seedsCoffea arabica L. indicate that rate of emanation of the inhibitor caffeine is highly enhanced during senescence of seeds, suggesting that when allelopathic potential of seeds is evaluated the presence of both young and old seeds should be considered. In many plants seeds are liberated close to the parent plant, the zone where seed-induced allelopathy may occur. Large numbers of seeds are usually produced in order to ensure establishment; greater number and mass of seeds may also increase allelopathic inhibition of competing vegetation.