FLOWERING IN ITS BIOLOGICAL FRAMEWORK 7 



idea of biological timing did not occupy the minds of many biologists 

 until the 1950's. 



It is now known that this phenomenon might be a general mani- 

 festation of virtually all living things. This cannot be stated as yet 

 with absolute certainty, but nearly all lines of evidence seem to 

 converge on this generalization. As we shall see in Chapter 8, 

 photoperiodism is only one of many examples of biological time 

 measurement. It has become a problem of fundamental importance, 

 and obviously the flowering process is an excellent example. 



4. Biochemistry 



Following time measurement (critical night), a flowering hormone 

 seems to be synthesized in the cocklebur leaf. Energy and proper 

 substrates are required. As mentioned above, the dark period is 

 ineff'ective unless it is preceded by a period of high intensity light — 

 a period of photosynthesis. The response to the light environment 

 also is biochemistry, since it is mediated through a pigment system, 

 although we might refer to this process as /7/zo/o-biochemistry (a 

 subdivision, perhaps, of photochemistry). 



The light response is a most interesting process from the bio- 

 chemist's viewpoint, since it apparently involves a trigger type 

 reaction. In photosynthesis the absorbed light energy is converted 

 to chemical bond energy, but in flowering the quantity of light 

 energy involved is extremely small, and rather than itself causing 

 flowering to occur, it turns the switch which then influences the 

 biochemistry of the flowering process. The remarkable fact is, that 

 in the case of the cocklebur or other short-day plants, turning the 

 switch during the dark period with light leads to an inhibition of 

 flowering, while in long-day plants this same switch promotes the 

 process. As we shall see in Chapter 7 the pigment system also 

 controls many other phenomena of plant growth. 



Action of the flowering hormone at the shoot tips must also be 

 biochemical, as is the very process of growth itself. Certainly 

 biochemistry is the spirit of modern biology. No other approach has 

 contributed so much in recent years. Thus it is somewhat disappoint- 

 ing to learn that virtually nothing is known with certainty about the 

 biochemistry of the flowering process. We have some ideas, and they 

 will be discussed in Chapter 9, but concrete and specific information 

 still belongs to the future. 



