Portugaliae Acta Biologica, Serie A. Morfologia, fisiologia, genetica e biologia geral 1949/51 pp. 729-84
Contribution to the physiology of development of the inflorescence and of the single flower (Bryophyllum and Kalanchoë).
Flávio Resende

Experiments conducted since 1945 on Bryophyllum daigremontianum [Kalanchoë daigremontiana] have shown that low light intensity affects flower initiation and development not directly but by acting on the auxin/antiauxin balance in the vegetative part of the plant. By varying only the light intensity falling on the leaves, every type of inflorescence and flower may be obtained, from the morphologically vegetative to the completely "floral". As the light intensity is increased, the flowers develop first calyx, then pistil, then corolla and finally androecium. This suggests that the calyx is the most vegetative part of the flower, requiring or tolerating the highest concentration of auxin, while the androecium is the most "floral" part. Although a low auxin/antiauxin ratio is required for the initiation and development of the inflorescence, in the inflorescence itself a greater amount of auxin is produced than in the vegetative parts of the plant, and it is this that causes the rapid growth of the floral parts. The internal correlation processes between the different plant organs during floral development are discussed with relation to B. daigremontianum and a species of Kalanchoë from Mozambique. It is concluded that there are no flowering hormones but that flowering is induced when a certain balance is reached by the hormones present in the plant in the vegetative state. The difference between short- and long-day plants lies in the existence or non-existence of a certain "limit to this hormonal balance".— Institute of Botany, Lisbon.