THE LOW TEMPERATURE PROMOTION OF FLOWERING 63 



chemically), although it has many of the biological properties of the 

 gibberellins, such as activity in the dwarf corn bioassay. It is inactive 

 in certain auxin tests (Avena curvature) but active in other typical 

 auxin responses (growth of sunflower tissue cultures). It will be 

 highly interesting to follow future work with this substance. 



The Theoretical Approach To Vernalization 



For many years now attempts have been made to discuss the 

 mechanisms of vernalization in physiological terms. Three basic 

 approaches to the problem are briefly summarized as follows : 



1. Antagonism Between Vegetative and Reproductive Growth 



Before any sort of formal work had begun on either vernalization 

 or photoperiodism, the theory had begun to develop that flowering 

 and vegetative growth are antagonistic to each other. It was deduced 

 that any means of repressing vegetative growth would result in 

 flowering. The general idea is still a part of much horticultural 

 practice, and often such a response may be observed. Plants are not 

 watered, not fertilized, pruned heavily, girdled or otherwise mutilated 

 to promote flowering. It was easy to apply the concept to vernaliza- 

 tion by saying that the inhibition of vegetative growth by cold 

 allowed reproductive growth to gain the upper hand. 



Yet as is often the case with such generalizations, the concept 

 proved to be highly over simplified. It only holds true for certain 

 plants. It is equally true for at least as many plants, including many 

 which require vernalization, that conditions which promote rapid 

 vegetative growth also promote flowering. The argument raged for 

 years around the concept of the carbohydrate/nitrogen ratio. It was 

 said that low nitrogen (obtained by controlling fertilizer application) 

 allowed a high development of carbohydrate and resulted in flowering. 

 Low nitrogen does seem to promote flowering in many species (e.g. 

 certain fruits), but this is not true for many other plants, where the 

 opposite condition seems to hold. For example, cocklebur is strongly 

 promoted in its flowering by high nitrogen levels in the soil — 

 providing that the proper day-length conditions have first been met 

 (Table 5-1). Thus there are no broad experimental grounds for the 

 idea that repression of vegetative growth leads to flowering. 



