Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


Three cultivars of Lilium longiflorum, Thunb., 'Ace', 'Nellie White' and 'Harson' were forced for the spring of 1983 and 1984 in greenhouse sections with minimum temperatures of 10, 14.5 or 18.9(DEGREES)C until 5 weeks after emergence (phase 1). Plants from each temperature treatment were then divided equally among the 3 temperature regimes (phase 2) to give 9 temperature histories. The design was based on results from a preliminary experiment in 1982. Fewer flowers, fewer leaves and shorter terminal height were associated with higher minimum temperatures. Flower and leaf number were most affected by early (phase 1) temperature treatment. 'Ace' produced more flowers and more leaves than 'Nellie White' or 'Harson'. 'Harson' was the tallest of the 3 cultivars followed by 'Ace' then 'Nellie White'. Temperature treatments did not influence the time required for the bulb to emerge from potting. The other growth stages: emergence to visible flower bud and flower bud to open flower took fewer days under higher temperatures. 'Nellie White' was quickest to reach the first visible bud stage from emergence when all cultivars had experienced 10(DEGREES)C in phase 1. Under all other temperature treatments, 'Harson' matured just as quickly as 'Nellie White'. 'Ace' was quickest to reach first open flower after the bud stage. Base temperatures were estimated for 'Ace', 'Nellie White' and 'Harson' Easter lilies by regressing change in plant height, change in leaf number and progress per day over 3 growth stages (the periods from potting to emergence, emergence to first visible bud and from first visible bud to first open flower) on temperature and determining the x-intercept. Using the estimated base temperatures, heat units were measured for all three cultivars from emergence to first open flower. 'Nellie White' gave the best uniformity in heat units for all three years followed by 'Harson' then 'Ace'. By substituting various base temperatures, it was observed that accumulated heat units from emergence to first open flower were most consistent across years when a base temperature of 0(DEGREES)C was used for 'Nellie White' and when a base temperature of 3.7(DEGREES)C was used for 'Ace' and 'Harson'.