528 C. Sironval 



It would be very useful to know if such a poisoning also occurs 

 in SD plants grown in long days. In Kalanclioe. blossfeJdinna, for in- 

 stance, the chlorophyll metabolism is undoubtedly different in short 

 or long days (37). If this corresponds to a decreased level of pro- 

 tection, a long day with relatively intense light is likeh to produce a 

 drastic photooxidation proportional to the length of the photo- 

 period. Perhaps the explanation of the dissymmetry revealed by GA 

 between the behavior of LD and SD plants is to be found here. Dur- 

 ing long days SD plants could withstand more severe metabolic in- 

 hibition of a photooxidative nature than coidd LD plants during 

 short days. GA would be able to overcome this inhibition in the last 

 case but not in the first. 



ACKNOWLEDGMENT 



The author is greatly indebted to the "Institut pour I'encourage- 

 ment de la Recherche Scientifique appliquee a I'lndustrie et a I'Agri- 

 culture, I RSI A," Beige, for financial aid. 



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