THE PHOTOPERIODICITY OF FLOWERING 



UNDER SHORT DAY WITH SUPPLEMENTAL 



LIGHT OF DIFFERENT WAVE LENGTHS 



by 



G. L. FUNKE t 



Late Director, Botanical Institute, University of Ghent 



From 1936 till 1940 in Ghent, Belgium, from 1941 till 1945 in Leyden, 

 Holland, and again since 1946 in Ghent, I investigated the effect of photo- 

 periodicity on flowering of a large number of plant species in different 

 ranges of wave length (3-13). The plants receive full daylight from 7 a.m. 

 till 3 p.m. ; for the rest of the day they are covered, partly by dark cases, 

 partly by white (limed), red and blue glass ; check plants remain in the open 

 air. The different sorts of glass transmit approximately an equal quantity of 

 solar energy. The place of experiment is such that during the hours when 

 the plants are covered, the sun does not shine directly upon the glass. Tem- 

 perature and humidity of the air under the glass cases, therefore, are only 

 slightly different from those outside; yet flowering under the white glass 

 is exceptionally a few days earlier than with the check plants, owing to a 

 little more favorable conditions during the night. The difference in time 

 of flowering due to the different wave lengths varies between 7 days and 

 more than 3 months. 



"Dark" or D means plants which get full day light from 7 a.m. till 3 

 p.m. ; "red" or R, "blue" or B and "White" or W means plants which are 

 exposed to full daylight from 7 a.m. till 3 p.m. and to red, blue and white 

 light respectively from sunrise till 7 a.m. and from 3 p.m. till sunset. 



Up till now I have examined more than 100 species and varieties. Some 

 species proved to be photoperiodically indifferent (group in the list) ; the 

 others can be divided into four groups according to their reactions, while a 

 few species behave in a way which so far I have not been able to explain. 

 My results deviate on the whole from those of other authors (1, 16, 17, 19, 

 21, 23, 24, 25, 26) ; as my way of experimenting is very different from 

 theirs, a comparison is hardly possible for the moment. 



Group I : [W-R] [B-D] : "red" flowers at the same time as "white," 

 "blue" at the same time as "dark" ; the flowering of long day plants is fa- 

 vored by a long white as well as by a long red day ; "blue" and "dark" hasten 

 the flowering of short day plants. 



It may happen that a long day plant develops a few flower buds in B, 

 which, however, decay or which, exceptionally, open after an abnormally 

 long time and develop crippled flowers (6, 8, 12) ; these flowers yield only 

 a few viable seeds if at all. A striking example of this phenomenon is pre- 

 sented by Anthemis tinctoria. This species is a LL-plant (2, 14, 18) which 

 needs a long red day for normal flowering, whilst a long blue day is hardly 

 sufficient for the formation of a few flower buds. I think this is the first case 



