INFLUENCE OF GIBBERELLIN AND AUXIN 347 



to prove this and also to assign it some specific place in the overall 

 process. But I do not feel that our present information is sufficient even 

 to permit us to make a guess. It seems to me particularly premature to 

 equate or connect the action of gibberellin with that of red or far-red 

 light. In lettuce seed germination, gibberellin causes the same response 

 as red light, that is, the seeds do germinate (Kahn et al., 1957). In 

 stem growth, gibberellin and far red have similar effects: they both 

 promote stem elongation; but here, at least in some cases, their effects 

 are clearly independent (Downs et al., 1957). As to flower formation, 

 it is readily induced by gibberellin both in typical "red-sensitive" and 

 typical "far-red-sensitive" plants such as spinach and radish, respec- 

 tively (Stolwijk, 1952; Wittwer and Bukovac, 1957a,b). Even if there 

 were more grounds for believing in a connection between the effects of 

 far red and red light and gibberellin, it could hardly be a close and 

 direct one, for it seems inconceivable that the small amounts of red 

 or far red which are needed for determining the response in some 

 plants can directly cause the appearance and disappearance of a 

 substance which is needed in the amounts gibberellin is needed for 

 flower induction. We would have to assume at least one intervening, 

 amplifying event. 



After having thus cautioned you against rash assumptions, I want 

 to take yet another step toward pinning down gibberellin action in 

 flower formation; but this may well be a step backward. When a cold- 

 or long-day-requiring rosette plant is induced in the natural way, by 

 cold or by long day, stem elongation and flower initiation occur almost 

 simultaneously. If these plants are treated with gibberellin, stem 

 elongation in most cases precedes flower initiation in a conspicuous 

 manner. There are exceptions to this rule; flower initiation seems 

 to be as early in gibberellin-treated Samolus plants as in long-day- 

 induced ones. Still, we must consider the possibility that the pri- 

 mary effect of gibberellin is on stem formation and that flower initia- 

 tion is brought about secondarily, the bolting (elongating) plant be- 

 coming capable of forming floral stimulus. This possibility is strength- 

 ened by the fact that gibberellin seems incapable of causing flower 

 formation in caulescent long-day plants (that is, long-day plants with 

 an elongate stem also in short-day conditions) (Lona, 1956b; Lang, 

 unpublished data). If this interpretation is true, we would still not 



