THE SYNTHESIS OF FLOWERING HORMONE 



181 



Figure 9-15 



Effects upon flowering of normal or low temperatures applied for 8 hr 



immediately following dark periods of different lengths. Effects are 



markedly different if five inductive cycles are used instead of one. Data 



previously unpublished. 



number of inductive cycles increases. They found that giving one 

 leaf 4 inductive cycles produces a higher Floral Stage than giving 

 two leaves 2 cycles. Of course, the sensitivity of cocklebur leaves 

 changes rather rapidly with time (see Figs. 5-4 and 9-3), and 4 cycles 

 given to the No. 3 leaf would be expected to be much more effective 

 than 2 cycles given to the No. 3 leaf and 2 cycles given to the No. 4 

 leaf. These workers also found that four long dark periods given 

 over a 10-day period with 2 long days between each inductive cycle 

 were less effective than 4 consecutive cycles. Again, as the leaf ages, 

 it loses sensitivity, and so this would be expected. Proper controls 

 could be used to see if these effects are real, but use of such controls 

 is not mentioned in the published paper. 



Schwabe (69), as mentioned above, has investigated the possible 

 participation of an inhibitor in the flowering process. He further 

 interprets his data as evidence for the formation of an adaptive 



