140 



THE FLOWERING PROCESS 



12 24 36 48 60 72 



TOTAL CYCLE LENGTH INCLUDING EIGHT HOURS OF LIGHT 



Figure 8-3 

 Flowering response of Biloxi soybean to 7 cycles including 8 hours of 

 light and different dark periods to provide the total cycle lengths as 

 indicated. The curve summarizes six highly uniform experiments 

 (standard errors for the summary points were less than ±0.45 at the 24, 

 48, 60, and 72-hr points). Data from Hamner (15). 



flowering is obtained only when the length of the dark period and 

 the length of the light period add up to approximately 24 hr or 

 multiples thereof. A summary of six of their experiments is shown 

 in Fig. 8-3. Bunning's theory explains the curves nicely, while any 

 sort of reaction sequence mechanism becomes quite complicated in 

 accounting for the 48- and 72-hr peaks in the curve. Interruption 

 experiments, such as that shown in Fig. 8-1, also often imply that 

 the light-dark pattern must match some internal oscillating sensitivity 

 to light or dark. 



Konitz' experiment, mentioned in the last chapter, showing 

 sensitivity to red during the dark period and far-red during the light 

 period, also is compatible with an oscillating timer which controls 

 the sensitivity to F-phytochrome (or perhaps R-phytochrome). 



2. Analogy with Persistent Orcadian Rhythms 



Circadian rhythms seem to be under the control of an oscillator 

 type clock. Thus the first evidence, the simplicity of the hour glass 



