Abstract
In this study, the growth periodicity of Cyrtanthus mackenii grown in unheated glasshouse was clarified and the effects of temperature on the initiation and development of flower buds were investigated.
1. A bulb shows a sympodial branching system, and each unit of the sympodial branch is composed of a membranous scale and 3 foliage leaves in 1/2 alternate arrangement from the base upwards and terminates in an inflorescence, which bears 5-7 florets. During the growing period from spring to autumn, repeated sympodial branching results in 2 inflorescences being initiated.
2. In the primary inflorescence, differentiation of the first floret progresses rapidly until the carpel margins fuse to form the ovary in August when further morphological development is suspended until November. The pollen mother cell attains the tetrad stage and the pollen grains mature and become functional between November and January. Anthesis occurs in late January through February. The secondary inflorescence initiated between July and September differentiates floral parts without suspension and comes into bloom in late April through May. Floral part of the tertiary inflorescence differentiates after a three-month delay following the secondary inflorescence, and will progress as described in the primary inflorescence.
3. Plants did not flower when they were moved from an unheated glasshouse to a heated one kept above 20°C on or before November 10. This result suggests that they have some chilling requirement for flowering.
4. When plants with inflorescences at carpel formation stage were exposed to chilling at 10°C for 3 weeks or 15°C for 4 weeks, and then shifted to a glasshouse kept above 20°C, they flowered normaly.
5. After the chilling requirement was fully satisfied, higher temperatures resulted in earlier flowering. However, some depression in the length of scape and the fading of flower colour were observed at 25°C.
