Factors controlling Flowering in the Chrysanthemum

Abstract

Inflorescence buds, produced by vernalized Chrysanthemum plants in long day, cease to grow, and die at an early stage if maintained in long day, but will produce open flowers if transferred to short day. Dissection of such buds reveals that development does not proceed beyond the formation of the bare receptacle and no florets are initiated, while inflorescence buds produced in short day have almost completed floret initiation when they become macroscopically visible. Inflorescence buds produced in long day can be induced to complete their development in long day by: removal of all lateral shoots, and by re-rooting the inflorescence itself, leaving only a number of bracts on its axis. Inflorescence buds produced in short day can be inhibited from developing by transfer to long day, transfer to low light intensity in short day, and application of auxin paste. All three methods of inhibition become progressively less effective with the advancing development of the bud. The latest stage at which development was found to have been arrested was that of ovule formation. Heights of plants were determined at budding and when the flowers had started to open; marked differences due to length of day were found. Teratological effects noted in buds, exposed for extended periods to long day, included formation of bracts on the receptacle (the absence of which distinguishes the subtribe Chrysantheminae of the Compositae to which the Chrysanthemum belongs) as well as secondary inflorescences, petaloid stamens, &c. The results are discussed in relation to known effects of auxin on vegetative growth and reproduction.