Production biological and anatomical background of essential oil accumulation in the developing fruits ofFoeniculum vulgareMill, subsp.vulgarevar.vulgare(chemovar.; anethole, chemoform; low anethole - low methyl chavicol) were studied. Nine different stages of development of generative organs were distinguished for analysis. It was proved by histological investigations, that oil ducts (vittae) are present in the early stages of development of generative organs, even at the time of bud formation, however their relative area (calculated to the cross section) shows maximum at the time of seed setting (53.6%). The oil yield shows its maximum (11.6%) at that special time and in the early development stages of fruits, when the relative ratio of oil ducts is high and the accumulation of the assimilates (development of endosperm) have not started yet. In contrary the oil yield calculated to one schizocarp is increasing up to the final ripening stages (0.787 μL/fruit) and the process can be described by saturation function. Upon analyzing the compositional changes of the oil, it was proved that the accumulation ratio of myrcene continuously decreased throughout development, while the fenchone content showed an opposite tendency, its ratio was 9.1% in the buds and increasing afterwards up to 23.2%. However, the amplitude of the compositional changes was a moderate one and there was no need to revise the former chemotaxonomical classification of the population.