A detailed study was made of primordia production on the main culm of the wheat cultivar, Triple Dirk, grown continuously in short days (8 hr), or in 0, 12, 20, and 28 short days before transfer to long days (16 hr), each at two levels of light intensity. For both light intensities plants in continuous short days produced the maximum number of primorida, and there was a mean reduction of 28, 31, 36, and 41 % in primordia in the treatments that received 28, 20, 12, or 0 short days before transfer to long days.