(Rosa hybrida) propagated by cuttings. II. Development time of "Sonia" miniplants in artificial light and temperature conditions. Cutting standardized stem pieces and rooting these under constant artificial conditions provided "miniplants" that could be grown in pots until the first flower, and which were practically free of season or storage effects. They were grown in controlled environment chambers with temperature and light control, in order to evaluate the effects of PAR irradiance and average air temperature, T, on the principal visible stages of development of the cultivar "Sonia". Four stages were defined (0 = release of bud inhibition; 1 = sprout length 1 cm; B = flower bud visible; F = beginning of anthesis), which determine 3 periods (0-1), (1-B), (B-F). The data analysed were as follows: the duration of each period; percentage of flower buds = % B; number of leaves on the stem = N. The duration of the period (0-1) was established with stipulary sprouts or regrowths, the duration of periods (1-B) and (B-F) with axillary sprouts (