196 THE FLOWERING PROCESS 



The approach has been followed by a number of workers, and the 

 summary data shown in Table 10-2 were assembled by J. P. Nitsch 

 at Gif-sur-Yvette (near Paris) based upon his experiments (29). It 

 seems fairly clear from our previous discussions that the changes in 

 auxin, gibberellins, etc., which accompany changes from short-day 



Table 10-2. Relative Growth Regulator Levels 



WITHIN Plants as Influenced by Environmental 



Factors 



Long days Short days 



1 . High auxins (Oat coleoptile 1 . Low auxins 

 promoters) 



2. High gibberellins (dwarf maize 2. Low gibberellins 

 bioassay), and Substance E. 



3. High auxin synergists (primarily 3. Low auxin synergists 

 inhibitors of lAA-oxidase, such 



as alpha-tocopherol) 



4. High leucoanthocyanins (colorless) 4. High anthocyanins 



(colored) 



5. Low inhibitors (coleoptile test) 5. High inhibitors 



Vernalizing cold treatments 



1. High auxins 



2. High gibberellins 



3. High sugars ; in some plant families at least, fructose and fructosans. 



4. High reducing substances such as glutathione 



5. Low inhibitors (coleoptile tests) 



Data from J. P. Nitsch (29). 



to long-day conditions or vice versa are probably not in themselves 

 responsible for the initiation of flowers. Yet these changes un- 

 doubtedly play important roles in development of the floral bud, 

 elongation of flower stalks, and probably the status of the flowering 

 hormone as discussed in this section. 



The Change From Making Leaves to Making 

 Flowers (8, 32, 37, 38) 



We can now return to the exciting problem introduced in Chapter 1 : 

 How does the flowering hormone cause a change in direction of 

 growth at the buds? The number of diverse and intricate forms 

 found among living organisms is astronomical. It took biology a 

 matter of two or three centuries just to describe these forms, and the 

 process is still going on. What is responsible for the many differences 



