182 THE FLOWERING PROCESS 



enzyme during successive inductive cycles. Again alternative 

 explanations are available. For example, he shows that once flowering 

 has been induced, nights shorter than those originally required for 

 flowering have a measurable promotive eff^ect on flowering (he used 

 Kalanchoe blossfeldiana, but a similar response is indicated in 

 Fig. 3-2). Is this because of adaptive enzyme formation, or do short 

 dark periods produce too little hormone to cause flowering, although 

 its eff'ect can be observed when it is added to some already present ? 

 Interactions of cycles or changes in the leaf in response to more 

 than the minimal number of inductive cycles have not been proven, 

 but the likelihood that they exist is great enough to merit our keeping 

 them in mind. 



The Synthesis of Flowering Hormone 



What does all this tell us about how the hormone is synthesized ? 

 Probably our researches have raised more questions than they have 

 answered, but even that may be productive ! 



There is excellent evidence that a flowering hormone exists, 

 although the picture is often complicated by the presence of inhibitors 

 as well as promoters. Hormone synthesis begins near the end of 

 time measurement, most effectively in the most rapidly expanding 

 leaves. The initial rate of hormone synthesis is not strongly influenced 

 by temperature; an unexpected finding that may lead to new ideas 

 about hormone synthesis. Later phases of the process are highly 

 temperature sensitive, and a destruction of hormone at high 

 temperatures is evident. 



Applied chemicals, especially antimetabolites, may help us learn 

 about the biochemistry of hormone synthesis. Time of application 

 experiments are essential to pinpoint the part of the process which is 

 being influenced, and since these are only possible with a plant which 

 will respond to a single inductive cycle, it is easy to see why cocklebur 

 and increasingly Japanese morning glory are emphasized so strongly 

 in this discussion. 



Such experiments have shown that respiration (ATP production) 

 is essential for hormone synthesis, and that amino acid (peptide 

 formation) and nucleic acid metabolism may be involved. There is 

 much to learn here, however, and we especially need clarification 

 about the specific roles of the leaf and the bud. This is the frontier. 



