136 THE FLOWERING PROCESS 



In view of all the difficulties which were encountered when one 

 attempted to apply Bunning's theory directly to the flowering process, 

 most workers began to feel that the theory was not a valid one. 

 Unfortunately, the real heart of the matter was largely overlooked : 

 Is timing in the flowering process controlled by an endogenous 

 oscillator or by the time required for various chemical reactions to 

 go to completion ? 



Is Timing in The Flowering Process Based Upon 

 AN Hour Glass Principle? 



Cycles occurring under non-varying conditions imply some sort 

 of oscillating timer, like a pendulum or a tuning fork. Biinning says 

 that plants contain such a system, causing them to oscillate with a 

 circadian period between a photophile and a skotophile phase. 

 Flowering in response to day-length is coupled to this system. The 

 alternative idea is that each dark (or light) period is measured by the 

 time required for the completion of a chemical reaction. As the 

 sand flows through the hour glass, so the metabolites flow through 

 the reaction sequence to measure time. Let us consider two strong 

 lines of argument in favor of the reaction rate or hour-glass clock 

 in the flowering process. 



1. The Simplicity of the Hour Glass Approach to an Understanding 

 of Timing 



Plant and animal functions seem to be mostly biochemical. 

 Contrasted with this approach, Bunning's theory of photophile and 

 skotophile phases sounds charged with mysticism. What is the nature 

 of these phases that makes light or darkness influence flowering ? In 

 the sense that physiology is the biochemistry of intact organisms, 

 Bunning's theory is hardly physiology at all. Assuming the theory 

 to be true, we are still faced with the problem of discovering the 

 reactions which account for the phases. The flowering process is 

 usually discussed, as it is in this book, in terms of a series of steps. 

 Why shouldn't time measurement simply be the time required to 

 complete the chemical reactions which make up these steps ? 



There is one serious problem attached to this approach. Biological 

 timing in flowering (as in most circadian rhythms, etc.) is relatively 

 temperature independent, whereas chemical reactions are highly 



