526 



RHYTHMS IN PLANTS AND ANIMALS 



.o^CONTROL 



4 8/2/6 20 2i 28 32 36 iO U 48 52 SS^rs 



Fig. 20. Biloxi soybean (short-day plant). Effects of light breaks (30 

 min) given at various intervals during long dark period. "Interaction" 

 of light break with main light period (reduction of flower formation) 

 only if both light periods fit into one period of 24 hr. Times of maximum 

 reduction a little more than 24 hr apart. (After Wareing, 1954.) Arrows 

 added by author of this paper. 



8 



/2 /6 2Q 24 28 22 36 LO U 48 62 56 hrs 



■*^^a— i^™^—— Mi^MgBM I 



Fig. 2L Hyoscyaimis niger (long-day plant). Effects of light breaks 

 (2 hr) at various intervals during long dark period. "Interaction" of light 

 break with main light period (promotion of flower formation) only if 

 both light periods fit into one period of 24 hr. Times of maximum 

 promotion 24 hr apart. Controls (without light break) are not flowering. 

 (After experiments of Claes and Lang, 1947.) 



