170 



THE FLOWERING PROCESS 



later time in the dark period ? Perhaps, but we seldom have time or 

 patience to apply a new compound at any time except the beginning 

 of the dark period. Another problem concerns the possible promotion 

 of the flowering process by a compound. If the dark period which 



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DAYS AFTER INDUCTION (time of treatnnent) 



Figure 9-11 

 Summary curves representing many experiments of the type shown in 

 Fig. 9-10. Chemicals which inhibit flowering have been found to be 

 effective when applied during either of the four periods, as shown by 

 curves A, B, C, and D. The A curve represents compounds which are 

 eff'ective only when applied before the end of the critical night (time 

 measurement); the B curve compounds which are eff'ective only when 

 applied before the end of the dark period (synthesis of flowering hor- 

 mone) ; the C curve compounds which inhibit if they are applied before 

 translocation of the hormone from the leaf is complete; and the D curve 

 compounds which inhibit floral development regardless of when they are 

 applied. In some experiments, the D curve and the development curve 

 may be nearly the same, indicating that the bud stops its development 

 completely at the time the chemical is apphed. Chemicals so far found 

 to be eff'ective in these experiments are summarized in Table 9-1. 



we use is so long that maximum flowering (saturation — part B of 

 the curve) is obtained, it may not be possible to observe a promotion. 

 Thus in recent years we have often used dark periods with lengths 

 in the A part of the curve. 



