THE LOW TEMPERATURE PROMOTION OF FLOWERING 65 



think of plant or animal function in terms of biochemistry. We now 

 know that photosynthesis, respiration, and many other plant func- 

 tions are the result of chemical processes going on within the cell. 

 This even applies to processes such as growth, which seem to be under 

 the control of hormones such as the gibberellins and auxins. Thus 

 it seems reasonable to imagine that vernalization might lead to some 

 chemical change within the plant which in turn leads to flowering. 

 This is the approach to an understanding of vernalization taken by 

 most plant physiologists. 



A problem immediately arises. How can low temperatures promote 

 the accumulation of a compound ? Chemical reactions are usually 

 speeded up by increasing the temperature and slowed down by 

 decreasing the temperature. The clue to the solution of the problem 

 may prove to be present in the phenomenon of devernalization, in 

 which high temperatures may inhibit flowering and reverse the 

 effects of low temperatures. It was suggested in the laboratories of 

 Gregory and of Melchers that two reactions were going on within 

 the plant. One is a synthesis of flower promoting substances; the 

 other a destruction of these substances : 



I III 

 A > B >D 



/II 



C ^ 



Reaction I, the synthesis, may proceed even at low temperatures. 

 Reaction II, the destruction, might go much more slowly at low tem- 

 peratures, but it might increase with increase in temperature much 

 more rapidly than reaction I. Thus at low temperatures B would 

 tend to accumulate, but at higher temperatures B would be destroyed 

 (converted to C — or perhaps back to A) before it could accumulate, 

 as illustrated in Fig. 4-4. At normal room temperatures B is further 

 converted to D, another step towards flower formation. D is not 

 destroyed by high temperatures, so after a few days devernalization 

 will not occur. Various other reactions may also be postulated to 

 account for subsequent day-length requirements when they occur. 



The theory is a neat one, but in a sense it is little more than a 

 graphic representation of the experimental observations. How does 

 it relate to present work with gibberellins and other extracts ? We 



