GROWTH SUBSTANCES-RED LIGHT INTERACTIONS 



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GA 

 R 



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GAl 

 R 



Fig. 3. Elongation of sections from dark-grown (Dg) or red-grown 

 (Rg) plants a"s affected by red light (R) treatment in the presence or 

 absence of IQ-^M gibberellic acid (GA). Dg sections 5 mm long, 1 mm 

 from apex. (Exp. 9-24-57.) Rg sections 8 mm long, 4 mm from apex. 



(Exp. 7-11-57.) 



of sections from dark-grown plants in both the presence and absence 

 of GA, and the absolute value of the inhibition was approximately the 

 same in both cases. In some experiments, the inhibition was slightly 

 but significantly less in the presence of GA than in its absence, but in 

 no case was it possible to prevent the red inhibition with any GA 

 concentration. No red-light inhibition was observed in the sections 

 from red-grown plants either with or without GA. 



Figure 4 shows the effects of 10^'M GA and of FR on sections 



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Dg 



FR 



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FR 



Rg 



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FR 



GA 



GA 

 FR 



Fig. 4. Elongation of 8-mm sections cut 4 mm from apex of dark-grown 

 (Dg) or red-grown (Rg) plants, as affected by far-red (FR) treatment 

 in presence or absence of 10~^M gibberellic acid (GA). (Dg exp. 3-25- 

 57; Rg exp. 4-5-57.) 



