Procedures are described for critical point drying the shoot apical meristems of Easter lilies for viewing in the scanning electron microscope. This preparatory technique was superior to either freeze-drying or the use of freshly isolated meristems. Photomicrographs of the morphological development of the entire shoot apex from the vegetative through several reproductive stages are presented. The morphology of a single flower is also illustrated.
Meristem diameter measurements revealed seasonal and bulb source variations. Diameter increased with increasing bulb size. When compared to non-cooled bulbs, low temperature treatments reduced meristem diameter prior to flower initiation. The average date of flower initiation of controlled temperature forced ‘Ace’ lilies over a 5-year period was January 21; whereas precooled lilies initiated about 1 week earlier. Greenhouse temperatures of 17−25°C accelerated the date of flower initiation when compared to 13°. A simplified technique for measuring the meristem diameter and observing the stage of development was developed.
The Easter lily forms 2 classes of primary flowers, initial and raised. They can also form secondary flowers. The number of initial primary flowers was correlated with meristem diameter. Larger bulb sizes resulted in a greater number of raised primary flowers. In general, only large bulbs formed secondary flowers. A greenhouse temperature of 13°C promoted the formation of raised primary flowers, while 21° promoted the formation of secondary flowers.
A measurement of the sprouting index showed seasonal and bulb source differences.
Potted ‘Ace’ lily bulbs were treated with gibberellic acid (GA3) as a soil drench using varying concentrations, numbers of applications and at different stages of development. There was no consistent effect on the forcing days to flower, plant height or the number of leaves, however, specific treatments with 1000 ppm significantly reduced the number of floral buds initiated. It appears that the most sensitive stage of application is that period just prior to flower initiation and that the GA3 must be applied at this time in order to reduce the number of floral buds initiated. A preliminary experiment indicated that GA4+7 was more effective than GA3. GA4+7 influenced plant height and leaf length as well as the number of floral buds but had no effect on the forcing days to flower.
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