THE SYNTHESIS OF FLOWERING HORMONE 



159 



6-0-- 



5-0 



UJ 



o 4-0 

 < 



cn 



< 3-0 

 o 



2-0- 



1-0 + 







Plants grown in 

 the greenhouse, 

 dark periods at IS'C 



O""'^ January 2, 1962 



8 9 10 II 12 13 14 15 16 

 NIGHT LENGTH 



Figure 9-2 



Two examples of curves showing flowering as a function of night 

 length. Both curves were obtained by placing plants in a growth 

 chamber at 15°C (see Figs. 9-5 and 9-7), but one curve represents 

 flowering of plants grown during the summer in the greenhouse and the 

 other curve shows flowering of plants grown in the winter in the green- 

 house. Part A of the curves is the steep part, during which synthesis of 

 flowering hormone appears to be very rapid, and part B shows the 

 period when hormone synthesis is relatively slow. Figures 9-5 and 9-7 

 show that the amount of hormone may even be decreasing during the 

 B part of the curve at higher temperatures (never, however, during the 

 A period). Data previously unpublished. 



that the rate of floral develoment is related to the amount of flowering 

 hormone that arrives at the bud, as discussed in Chapter 5. 



Leaf Growth and Sensitivity to Induction 



Figure 5-5 in Chapter 5 shows the results of an experiment in 

 which cocklebur leaves of diff'erent ages are given an inductive dark 

 period. We concluded that the No. 3 leaf is most capable of synthe- 

 sizing flowering hormone. Figure 9-3 shows the same flowering data 

 along with the square of the lengths of the various leaves, plotted as 



