Abstract
The growth periodicity of Hymenocallis plants grown outdoors and the effect of temperature on the initiation and development of flower buds were investigated.
1. Hymenocallis bulbs have a sympodial branching system with each unit of the sympodial branch consisting of a membranous scale and about 17 foliage leaves in 1/2 alternate arrangement from the base upwards. The apex terminates in an inflorescence bearing about 5 florets.
2. Shoot apices of plants grown outdoors were in the vegetative state in early October; they began to flatten and broaden in early to mid-October. Subsequently, the outer and inner tepal primordia of the first floret appear by the year's end. Further development of flower buds is resumed in late April when stamen initials appear. In early June the carpel primordia of the first floret of an inflorescence become evident. Pollen formation occurs in early or mid June and the flower blooms in early August.
3. Flower formation was inhibited when plants were held at 25°C after 1 July but it was promoted when plants were transferred to 15° or 20°C. After flower buds were initiated, plants kept at 25°C flowered earlier but they had smaller florets and shorter scape length than did those held at the cooler temperatures.
4. In a commercial forcing trial, flowering in late May, which is two months earlier than the natural flowering time, was attained by keeping plants at a min. of 20°C after the end of November. Moreover, by exposing plants to a photoperiod of a 16-hr day and maintaining them above 20°C from the end of September, the plants bloomed in mid-April.
