346 



GROWTH FACTORS AND FLOWERING 



Fig. 4. Induction of flower formation in short-day-grown Silene armeria 

 by treatment with gibberellin. From left to right: controls; plants treated 

 with 2, 5, 10, 20, and 50 /xg of gibberellin daily. Flower formation oc- 

 curred only with the two highest dosages. The plants on the extreme right 

 are about 1.5 meter high. 



inductive process. We know that this process is a composite of several 

 "partial reactions" (see above), and that some of these reactions are 

 promotive with respect to flower formation, while others are inhibitory. 

 Gibberelhn seems to be one of the promotive elements in the overall 

 process, but its effect will depend on the efficiency of the other reac- 

 tions and on their balance. In some plants gibberellin may be actually 

 the limiting factor in flower induction; such plants will respond to 

 applied gibberellin with prompt flower formation. However, in other 

 plants of the same response type the balance of the partial reactions of 

 induction may be different; another partial step may be more critical 

 than gibberellin; gibberelHn application will have little effect on 

 flower formation, and may have none at all. 



All this sounds rather general, but I do not want it to sound other- 

 wise. If our basic idea is right, and gibberellin, in contrast to auxin, is 

 directly involved in the light reaction process, it must in some man- 

 ner be tied in with the photoreaction of this process, and we shall have 



