174 THE FLOWERING PROCESS 



substrates such as sugar were essential for flowering. This of 

 course agrees with the conclusions of experiments using respiration 

 inhibitors. 



B. Amino acid antimetabolites. Results with some com- 

 pounds that inhibit during the hormone synthesis part of the dark 

 period are not easy to interpret. For example, a number of com- 

 pounds were tried which are known to interfere with the synthesis 

 of protein. Most of these amino acid analogs turned out to be 

 ineffective, and we were then tempted to conclude that protein 

 synthesis was not a part of flowering hormone synthesis. One 

 compound (ethionine) was found which might inhibit protein 

 synthesis, although other interpretations were also possible. Some 

 time later another very eff"ective protein inhibitor (p. fluoro- 

 phenylalanine) proved to be active in our tests. The corres- 

 ponding amino acids will reverse the eff"ects of these inhibitors. 

 At the time this is being written it would probably be unwise 

 to draw any definite conclusions about the matter, but it surely 

 seems possible that peptide bond synthesis is a part of flowering 

 hormone synthesis after all. Is it possible that the flowering 

 hormone consists of a peptide made up of only a few amino acids ? 



C. Other compounds. A number of other compounds inhibit 

 flowering only if they are applied during the last half of the 

 inductive dark period or before. In some cases (for example, 

 quercetin) we have little information about how these com- 

 pounds might be influencing metabolism, but others are known to 

 inhibit nucleic acid metabolism. Since nucleic acids are known to 

 participate in the control of growth and form we were initially 

 very excited upon finding these compounds and discovering that 

 the time of inhibition is the time of flowering hormone synthesis. 

 Again, however, the picture has become quite complicated, and 

 for some years now we have been at a loss to understand all of 

 the implications. 



The main compUcation arises through the observation that 

 5-fluorouracil (an analog of uracil or thymidine) inhibits flowering 

 when appHed to the bud as well as when applied to the leaf. Yet 

 by our definition, hormone synthesis must be taking place in the leaf. 

 Thus if 5-fluorouracil (5-FU) is active only in the bud, then its action 

 must be related to transformation of the bud to the reproductive 

 condition (to be discussed in the last chapter) rather than to hormone 



