Abstract
Delphinium 'Blue Bird' seedlings exposed to low temperatures below 9 °C flowered rapidly when the air temperature was increased. When seedlings were not exposed to the low temperatures, flowering was delayed but eventually all the seedlings flowered in the summer. The chilled seedlings did not differentiate flowers during the chilling periods. The results inidicate that flower differentiation does not occur under low temperatures but under high temperatures and the critical temperature for flower differentiation is lowered by exposure to low temperatures. Increasing the chilling duration hastened flowering, indicating that the effect of low temperatures on the flower differentiation is quantitative.
