INTERACTION OF LIGHT INTENSITY AND TEMPERATURE IN THE FLOWERING OF APHELANDRA SQUARROSA NEES
These findings were substantiated by Herklotz (1965) who conclusively showed that flowering in Aphelandra is limited by the daily amount of light (intensity x duration of illumination), whereas day-length has no effect. Both Rünger and Herklotz (1.c.) found that high temperature promotes flower formation and development under high light intensities. On the basis of his own studies and unpublished work by Maatsch and Rünger Herklotz concluded that "Eine Verschiebung der induktiven kritischen Wertes der Lichtmenge unter dem Einfluss der Temperatur findet offen-bar nicht statt".
The studies reported on here were started in 1961 at the Department of Floriculture. A preliminary report of some of the results has previously been given (Heide and Hildrum 1966).
For these first experiments the cultivar 'Fritz Prinsler' was used (see Bosse 1962). Parallel treatments were given in artificial light in growth chambers and in day-light in greenhouse compartments according to the following scheme:
Growth chambers 12,15, 8, and 21°C 9 and 24 hr. constant temperature day-length
Greenhouse 12,15,18, and 21°C 9 and 24 hr. night temperature day-length
Experiment started on July 10.
The results of the greenhouse experiment were in accordance with those reported by Rünger and by Herklotz: flowering was promoted by high temperature under summer light condition. Day-length on the other hand had no effect (table 1).
In artificial light (about 3500 lux from Philips TL 33 fluorescent tubes for 9 hrs. daily) the plants responded in a different manner: no flower buds were visible at any temperature or day-length when the greenhouse experiment was terminated after 21 weeks (November 27). The plants were then moved into a greenhouse with 21°C minimum temperature and natural day-light supplemented with weak (about 50 watt/m2) incandescent light throughout the night. After about 10 weeks under these conditions