Crecimiento de tubos polínicos y eficiencia reproductiva en acacia glomerosa benth. (mimosoideae)

three trees of a natural population of acacia glomerosa were studied. the following sexual reproduction variables were measured: number of flowers by inflorescence, number of stamens per flower, number of polyads per stamen, number of pollen per polyad, number of gynoecia with viable and no viable polyads, and numbers of pollen tubes per viable polyad growing at the styles (tpp). the number of fruits per inflorescence, number of seeds per fruit and number of ovules per ovary were also measured. it was found that the pollen/ovule ratio was 3699.14, the seeds/ovule ratio was 0.81 (seed-set), and the fruits/flower ratio per head was 0.08 (fruit-set). these two last ratios show that the total of ovules that produces a plant, only 6.5% (seed-set × fruit-set × 100) becomes seeds in natural pollination. not only the high pollen/ovule ratio, but also the low percentage of ovules that becomes seeds, are coherent with the results of the most of the allogame species. the study of the stigmas in natural pollination reveals that 35% were not pollinated, and from those which were pollinated about 39% contained no viable polyads. these results might indicate that the pollinators in the population are limited, without finding important differences among the three trees studied. the moderate sterility of the polyads or the gynoecias, are both factors limiting the fruit-set. when the stigmas receive a viable polyad, a high percentage of pollen grain fertilizes the ovules of the ovary. this increases the number of seeds in the ripe fruits (ca. 80% of the ovules of ovary becomes a seed).