Flowering of hemp (Cannabis sativa) occurred on photoperiods that ranged from 8 to 20 hours of light per day, but at photoperiods of 16 to 20 hours flowering was incomplete and very greatly delayed. Seedlings only 3 weeks old flowered promptly when shifted from 16-hours to 8-hour photoperiods. Flowering in 2-branched plants in which one branch received long and the other short photoperiods was restricted to the branch that received short photoperiods. Temperatures, as low at 55[degree]F during the dark periods did not prevent floral induction but a very low level of light equivalent to about 0.03 ft.-candle from an incandescent filament lamp during the 16-hour periods between daily 8-hour photoperiods was inhibitory to flowering. An abundance of "female" seed was produced by pollinating female flowers with pollen from male flowers produced on female plants. Studies of the effects of environmental factors such as nitrogen nutrition, light intensity, changes in duration of photoperiod and variations in temperature were made on the numbers and rates of development of male flowers produced by the female plants derived from this seed. High intensity light during the photoperiod, abrupt transfer of plants from long to short photoperiods, and relatively low temperatures during the dark periods resulted in increased production of male flowers by female plants. Hereditary differences were observed in the extent to which female plants produced male flowers.