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chapter six t chemical Control 



of Flowering 



Attempts to bring about or prevent flowering by the applica- 

 tion of chemicals are carried on for both practical and theoretical 

 reasons. The former are self-evident, the latter hardly less so. As 

 already indicated, studies on the mechanism of induction have 

 included work with various metabolic inhibitors, which will not 

 be considered further here. More attention has been paid to the 

 effects of naturally occurring compounds and of other substances 

 that modify plant growth; variations in the supply of various 

 minerals have also been studied with respect to flowering. 



A major motive of this kind of work has been the hope of 

 discovering compounds, either naturally occurring or synthetic, 

 with florigen activity. Although there have been reports of success 

 from time to time, none of these has as yet proved valid. Either 

 the work has been unrepeatable or the substance in question has 

 not fulfilled the criteria for florigen. Drawing on the previous 

 chapter, the minimal requirement for such activity is the ability to 

 bring about flowering both in LDP^ under short days and in SDP 

 under long days, as well as in cold-requiring but un vernalized 

 plants. In addition, if the substance is to be considered a true 

 (naturally occurring) florigen, it should of course be produced 

 only under inductive conditions. It is well to keep these criteria 

 in mind, since the effects of the first class of compounds to be con- 

 sidered are dramatic enough to be misleading in this regard. 



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