The ratio of male to female flowers (sex ratio) in the monoecious Croton bonplandianum Baill decreased as plants aged in three habitats. Two major forces, male and female gametic success and intra-sexual selection, have been invoked to explain the decrease in sex ratio. While increasing female gametic success at successive stages of growth might be responsible for the enhanced allocation of resource to the females and hence for the absolute increase in number of female flowers at a later age, increasing male gametic success does not change the absolute number of male flowers but merely causes an increase in the number of pollen grains deposited on the stigma. Differences in the sex ratio between habitats was influenced by the differential fitness gained by the two sexes in the various habitats
