This study was undertaken to determine the time-course of floret primordium initation and degeneration in relation to thermal time after sowing in various cultivars and tiller position sof wheat (Triticum aestiveum L.). The field experiment was carried out on the experiment station of Nanjing Agricultural University of China. and included three sowing dates: carly planting of 30 September. middle planting of 30 October and late planting of 2 march and two wheat cultivars: winter type 'Jing 411' and spring type 'Yangmai 158'. Quadratic and linear relationships could deseribe floret initiation. degeneration and abortion in response to growing-degree-days after sowing for main stem and first and second tillers of middle planting plants of both cultivars. The floret fertility. The growing-degree-days from sowing to floret intiaion were significantly diffeent between the thre sowing dates and between the two cultivars. These results help quanitfy the dynamic processes of apical development and explain differcnes in floret development of wheat with different environments. cultivars and tiller development and explain the diffences in floret development of wheat with different environments. cultivars and tiller positions.