114 



6 -op 



THE FLOWERING PROCESS 



1 1 ; \ r 



Interruption time (I6hr dark period): 



10- 12 60 



SECONDS OF RED LIGHT INTERRUPTION 



Figure 7-5 



The effects upon flowering of light interruptions given for various 

 durations at various times after the beginning of a 16-hr dark period. 

 Saturation time is about 6 sec, but when the interruption is given at 8 hr 

 a maximum inhibition is obtained with only slightly more than 2 sec. 

 It is unlikely that the 8-hr interruption time measures saturation of the 

 pigment system. Data from Frank Salisbury and J. Bonner, 1956, 

 PlantPhysiol. 310, Ul-Ul. 



reciprocity relationship no longer holds. I have made a few attempts 

 to study the relationship at extremely high intensities and very short 

 durations, using an electronic flash built for photography. Such a 

 light produces extremely high intensities for durations in the neighbor- 

 hood of 1 /5000th of a second (a single flash will inhibit flowering 

 markedly when the light is held a few centimeters away). PreUminary 

 indications were that reciprocity does indeed fail under such 

 conditions. 



2. Light Interruptions Applied at Various Times 



Many workers using many species have studied the times during 

 the dark period when a light interruption is most effective in inhibi- 

 tion of flowering in short-day plants, or promotion in long-day plants. 

 The experiment is a relatively simple one. A light source of adequate 



