THE SYNTHESIS OF FLOWERING HORMONE 



179 



Control 



'noon midnight noon midnight 

 treatment time after induction 



Figure 9-14 

 Effects upon flowering of defoliation at various times following a 16-hr 

 inductive dark period, using control plants and plants treated with auxin. 

 Results are typical of five experiments. Data from F. B. Sahsbury, 

 1959, in R. B. Withrow, Photoperiodism and Related Phenomena in 

 Plants and Animals, pp. 381-392, American Association for the Advance- 

 ment of Science, Washington, D.C. 



5. Compounds Which Inhibit Floral Development 



Table 9-1 lists a few compounds which inhibit flowering regardless 

 of when they are applied — even if plants are treated just one or two 

 days before the buds are examined. Growth of the flower bud seems 

 to be stopped in its tracks by these substances. The compounds 

 listed are mostly herbicides, so perhaps the response is not surprising. 

 2,4-D is also considered to be an auxin, but in flowering it acts as an 

 auxin only at very low concentrations. 



6. Hormone Synthesis before the end of the Critical Night (32) 



Although the biochemistry of time measurement and synthesis of 

 flowering hormone seem to be clearly different, it is not out of the 

 question that the two processes might overlap for an hour or so. 

 Three kinds of experiments may be interpreted as indicating that 

 this is the case. First, applied antiauxins will promote flowering 

 under threshold conditions, and it has been reported that they will 



