FLOWERING HORMONE MOVEMENT AND ACTION 



185 



80 

 70 

 60 

 5-0 

 40 

 3-0 

 20 

 10 

 



S'— 



16 24 36 48 60 72hrs 9days 



TREATMENT TIME AFTER BEGINNING OF THE DARK PERIOD 



Figure 10-1 



Effects on flowering of cocklebur of defoliation at various times and 

 temperatures following an inductive dark period. After 16 hours in the 

 dark at 28 to 29.5X (beginning September 27, 1962), plants were trans- 

 ferred to growth chambers at the temperatures shown for 52 hr, after 

 which they were returned to the greenhouse. Plants were defoliated 

 while in the growth chambers at the times shown. Approximate half 

 times for translocation of the flowering stimulus from the leaves are: 

 9X = 62 hr after beginning of the dark period; 16° = 32 hr; 23° = 26 hr; 

 and 30° = 32 hr. As temperature increases towards 23°C, Gio for trans- 

 location decreases from about 2.5 to about 1.5. Data previously un- 

 published. For similar results with Japanese morning glory, see 

 Zeevaart (37). 



branch is induced to flower and the time required for the other branch 

 to flower is measured. Such methods are also at best only estimates. 

 They seem to agree, however, that the rate of movement of flowering 

 hormone is exceptionally slow, in the neighborhood of 2 to 4 mm 

 per hour. Sugars produced by photosynthesis in the leaf are known 

 to move through phloem tissue at much faster rates in many plants 

 including cocklebur, usually between 200 and 1000 mm per hour. 

 A number of experiments have indicated that flowering hormone 

 moves in the same direction as the sugar, and movement of the 

 hormone may be dependent upon movement of the sugar (see 



