340 GROWTH FACTORS AND FLOWERING 



Unfortunately, this hypothesis will not be easy to test, for the 

 flowering response does not lend itself to the precise quantitative treat- 

 ment which would be necessary for such a test. And on second thought, 

 perhaps this is not so unfortunate at all. For would even a complete 

 explanation of the auxin and antiauxin effect on photoinduction in 

 long-day plants contribute to our understanding of the induction proc- 

 ess itself? I am dubious about this, for the same statement can be 

 made about the effect of auxin on photoinduction in long-day plants 

 as had to be made in short-day plants. The effect seems to be a 

 strictly quantitative one. If the auxin or antiauxin treatment is done 

 under strict short-day conditions, without any supplementary light, 

 that is, if we are in the qualitative range of photoinduction, no flower- 

 ing response whatever is obtained (see Table III). If, on the other 

 hand, the intensity of the supplementary light is raised to a saturating 

 level and all plants initiate flowers, auxin has no promotive effect 

 either, its only influence being inhibition of flower formation by 

 relatively high concentrations. Auxin thus does not seem to be a 

 decisive factor in photoinduction of long-day plants either; it seems 

 rather to be able to modify the effectiveness of induction within a 

 fairly narrow range of specific light conditions. 



Postinductive and Preinductive Auxin Effects 

 in Short- and Long-Day Plants 



The auxin picture in relation to photoinduction is complicated by 

 the fact that in addition to the auxin effects about which I have spoken 

 so far, and which seem to be on induction itself, there are some other 

 auxin effects on flower formation which may be superimposed on the 

 induction effects. I have mentioned before, that, according to Salisbury 

 (1955), auxin which is applied after the floral stimulus has left the 

 leaf may promote flower formation. This promotion is most evident 

 when the postinductive light conditions are not too good. An ap- 

 parently similar effect has been observed by Leopold and Thimann 

 (1949) in a long-day plant, Wintex barley. These authors found that 

 auxin application increased the number of spikelets formed upon long- 

 day treatment. They interpreted this as an effect on induction, but 

 Hussey and Gregory (1954) showed that it is an effect on the develop- 

 ment on the initiated spikelets which goes hand in hand with enhanced 



