Progress？o da flora？？o e antese de Allium cepa L. (Alliaceae) em Candiota, RS, Brasil

the necessity for pollination by insects depends on the morphology of the flower, the degree of self-fertility and the arrangement of the flowers. we studied the progression of the flowering of allium cepa l., by measuring the frequency of visits by apis mellifera l., the anthesis phase and pollen viability. the flowering period in the cultivar crioula (56 days) was longer than in bola precoce (50 days). the duration of the peak of flowering was similar in both cultivars, 15 and 17 days respectively. the correlation between the frequency of visits by a. mellifera and the number of umbels with open flowers was high in crioula and average in bola precoce. the anthesis occured at 7 and 8 days respectively in the two cultivars. contrary to other observations, we have verified incomplete protandry in both cultivars. stigmas were receptive when the styles had reached a length of 4-5.5 mm. the average percentage of pollen viability was 90.46 (crioula) and 80.25 (bola precoce).