INFLUENCE OF GIBBERELLIN AND AUXIN 339 



(Lang, unpublished data) that antiauxins influence photoinduction in 

 Hyoscyamus in much the same manner as auxins, a finding which 

 renders the above explanation rather improbable. An example of this 

 effect is shown in Table III, and Table IV lists the auxins and antiauxins 



Table IV. Effect of Applied .\uxins and Antiauxins on Photoinduction in Annual 

 Hyoscyamus (Plants were given short days with weak supplementary light 



during night periods) 



Auxins Antiauxins 



Promotion at Relatively Low Concentrations, Inhibition at Higher Ones 

 3-IndoIeacetic acid 2,3,5-Triiodobenzoic acid 



3-Indolebutyric acid 2,6-Dichlorophenoxyacetic acid 



a-Naphthaleneacetic acid 2,4,6-Trichlorophenoxyacetic acid 



/'-Chlorophenoxyisobutyric acid 

 2,4-Dichlorophenoxyisobutyric acid 

 2,4-Dichloroanisol (weak effect) 

 2,4-Dichlorophenetol (weak effect) 



No Promotion; Inhibition at Higher Concentrations 

 3-Indolepropionic acid Skatol 



/3-Naphthoxyacetic acid 

 2,4-Dichlorophenoxyacetic acid 



which promoted the flowering response in Hyoscyamus plants receiv- 

 ing subsaturating intensities of supplementary light. The few negative 

 cases are probably without significance, indolepropionic acid being a 

 rather weak auxin, y8-naphthoxyacetic acid and 2,4-D producing 

 injurious effects which would mask any flower-promotive action that 

 might be present, and the inactivity of skatol probably being a question 

 of insufficient penetration. The salient point in Table IV is that at least 

 3 auxins and 5 to 7 antiauxins had a similar promotive effect on photo- 

 induction in Hyoscyamus. 



Auxin and antiauxin producing the same effect is not easy to ex- 

 plain, particularly since in short-day plants they seem to obey law 

 and order, antiauxin offsetting the effect of auxin (see Table II). One 

 explanation is that auxin inhibits photoinduction in long-day plants 

 just as it does in short-day plants, but that the endogenous auxin in 

 long-day plants is at a level which is already optimal for this effect. 

 In this event, both the addition of auxin and of antiauxin would 

 reduce the auxin effect, that is, lower the degree of inhibition and thus 

 promote flower formation. 



