GROWTH REGULATORS AND COCKLEBUR FLOWERING 383 



plies the truth of the other. Thus evidence relating to either assumption 

 would be valuable, and such evidence obtained from translocation ex- 

 periments is presented below. 



Second High-Intensity Light Process 



Lockhart and Hamner (1954) have shown that flowering hormone 

 produced during an inductive dark period may disappear unless this 

 dark period is followed by a period of high-intensity light. Thus they 

 have postulated a stabilization of flowering hormone by high-intensity 

 light, and this has been referred to by Liverman (1955) as the second 

 high-intensity light process. 



Translocation 



After the flowering hormone has been synthesized in the leaf it must 

 be translocated to the bud where differentation of floral primordia will 

 occur. The movement of flowering hormone can be measured by de- 

 foliating the plants at different times following a single inductive dark 

 period (Khudairi and Hamner, 1954; Salisbury, 1955). It has been 

 found that if plants are defoliated immediately after the dark period, 

 the apical meristems remain vegetative. If, however, plants are defoli- 

 ated a number of hours after the inductive dark period, the apical 

 meristems develop into floral primordia at a rate comparable to that of 

 plants which have not been defoliated. Intermediate times of defolia- 

 tion result in intermediate rates of floral development. This observa- 

 tion is in harmony with the assumption mentioned above that the rate 

 of floral development is a function of the amount of flowering hormone 

 which reaches the bud, and thus it adds support to the assumption that 

 the amount of hormone produced is a function of the length of the dark 

 period. 



Differentiation 



The primary meristems respond to the flowering hormone by differ- 

 entiating into floral primordia. 



Development 



The floral primordia develop into flowers and eventually into fruits. 

 Of course a number of differentiation steps also take place during this 

 period. 



