GROWTH REGULATORS AND COCKLEBUR FLOWERING 385 



determine the rate of floral bud development. This is shown as a solid 

 line. 



It can be seen from the composite curves of Fig. 1 that 2,4-D, 

 maleic hydrazide, and Dalapon inhibit flowering even when they are 

 applied only 1 or 2 days before buds are examined. Thus, it would 

 appear that these compounds inhibit the development of floral buds. 



I 23456789 



Days after Long Dark Period 



Fig. L The inhibitory effect of various growth regulators upon flower- 

 ing as a function of their time of application. The black bar at the left 

 side of the abscissa represents the single inductive dark period. CN 

 indicates the critical night portion of this period, and HS represents the 

 hormone synthesis portion. The S-shaped solid line is typical of results 

 obtained in translocation (defoHation) experiments, and the other slanted 

 solid line indicates the relationship between floral stage of untreated 

 control plants and days following the inductive dark period (develop- 

 ment). The broken lines summarize 13 experiments using the indicated 

 growth regulators at more than one concentration in each experiment 

 (Salisbury, 1957b). 



Indoleacetic acid and naphthaleneacetic acid (the auxins), however, 

 inhibit flowering only when they are applied to plants before the 

 flowering hormone has been translocated from the leaf. Thus, it would 

 appear that these compounds influence flowering either by interfering 

 in some way with the translocation of flowering hormone or by de- 

 stroying flowering hormone in the leaf. Dinitrophenol appears to in- 



