TIMING AND THE FLOWERING PROCESS 



35 



100 



? 80 -f 



Ut 



o 



^ 60 



Q 



o 40 



20 



Controls : 

 72 hrs. 



24hrs. 



12 24 36 48 



HOURS AFTER BEGINNING OF THE CYCLE 



Figure 8-1 

 Flowering response of Biloxi soybean to 4-hr light interruptions applied 

 at various times during a 64-hr dark period. The data are indicated by 

 horizontal lines which show the 4-hr duration of the interruption. 

 Plants received 7 cycles of 8-hr light followed by 64 hr darkness, as 

 indicated by the bar at the bottom. Postulated photophile and skoto- 

 phile phases are also shown by light or dark bars on the bottom. Data 

 from Hamner (15). 



of delay in their leaf movement activities. On the basis of this it was 

 possible to successfully predict whether or not each variety should 

 be a short-day plant or a day-neutral plant. On the other hand, 

 P. F. Wareing in England found with Biloxi soybean and cocklebur 

 that there was no relationship between the effectiveness of a light 

 interruption of an inductive dark period and the time of the previous 

 onset of the light period. Interruptions coming near the end of a 

 dark period might be inhibitory even if they fell in what might be 

 predicted to be the photophile phase. Bunning again pointed out 

 that some plants such as cocklebur were set in their phases by the 

 onset of darkness rather than light, but this failed to explain some of 

 the situations which Wareing and others had discovered. Bunning 

 himself found that some short-day plants and long-day plants 

 exhibited the same photophile or skotophile characteristics at the 

 same time of day. This was probably the most serious retreat which 

 he was forced to make. 



