FLOWERING HORMONE MOVEMENT AND ACTION 189 



along with the sugar. Searle's experiment may mean that it is not so 

 much a matter of moving with the sugar as it is having an ample 

 supply of sugar to activate the movement. Tracer studies should be 

 done with Searle's arrangement to clarify this matter. 



Unfortunately, Searle concludes in his discussion that the status 

 of the hormone as well as its translocation is independent of light 

 conditions following the dark period, even though the majority of 

 his experimental plant was left in the light all the time ! Zeevaart (38), 

 in discussing these results in a recent article, implies that there never 

 really is an effect of light conditions following the inductive dark 

 period, even though a number of papers by Lockhart and Hamner 

 and various other workers clearly demonstrate such effects. Zeevaart 

 further implies that since Searle's conditions were controlled, his 

 results must take precedence over all others. Can we really put that 

 much faith in controlled conditions ? 



It should be quite evident from Figs. 9-1 and 10-1 that there is 

 considerable variation in times of translocation from the leaf. This 

 is undoubtedly due to environmental influences (the genetics of the 

 plants were the same in all experiments), and studies with controlled 

 environments should be directed towards understanding the nature 

 of these influences. Just because no variability shows up when 

 experiments are done under one single set of conditions, we should 

 not conclude that results under those conditions are typical of 

 flowering in general. ^^ The typical controlled environment is an 

 extremely artificial situation anyway. Light quality and intensity 

 differ markedly from natural conditions. In studies on different 

 photoperiod lengths, the continuous high light intensities provide 

 different photosynthesis times as well as different durations of light. 

 In short, we must take care in using this valuable new tool. 



At any rate we might conclude that if a leafi^ is stopped from 

 making hormone by a light interruption (producing F-phytochrome) 

 and is then left in the dark or low intensity light until its carbohydrate 

 supply is diminished (and not supplied artificially with sugars), then 



" For example, under a given set of temperatures and light intensities, we can 

 repeatedly observe about a 2-fold promotion in Floral Stage in plants treated 

 with the inhibitor 5-FU. Since most experiments with 5-FU show an inhibition, 

 we would be rather unwise to conclude that 5-FU is a general flowering promoter. 

 Our problem is to try to understand these unexpected results. 



^^ The effect of light intensity following the dark period is clearly on the leaf 

 and not the bud. 



