Flower size generally decreases as temperature increases. The objective of this research was to investigate during development when flowers of Campanula carpatica Jacq. `Blue Clips' and `Birch Hybrid' are sensitive to temperature by conducting two temperature-transfer experiments. In the first experiment, plants were grown initially at 20 °C and then transferred at visible bud to 14, 17, 20, 23, or 26 °C until flower. In the second experiment, plants were transferred from 14 to 26 °C or from 26 to 14 °C at 1, 3, or 5 weeks (`Blue Clips') or at 1, 2, or 3 weeks (`Birch Hybrid') after flower induction. Temperature before visible bud had little effect on final flower size for both species. For example, flower diameter of `Blue Clips' was similar among plants grown at constant 14 °C or grown at 20 °C initially and then transferred at visible bud to 14 or 17 °C. Similarly, flower diameter of plants grown at constant 26 °C was similar to those grown at 20 °C initially and then transferred at visible bud to 26 °C. Flower diameter in these species is correlated with the temperature after VB in the 14 to 26 °C and decreases linearly as the temperature after VB increases.
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