544 



RHYTHMS IN PLANTS AND ANIMALS 



2000 

 1000 

 500 



200 



100 

 50 - 



20 - 



10 



Si 



© 



NORMAL 



REACTIVE 



PERIOD 



Dose ierqs/mm^) 



O^ 



--«— 4500 

 --«-- 6000 



I 



I 

 UV| 



. .*. I . . 



.1 . .. I 



il.M, 



24 4 8 



12 

 PhTR 



16 20 24 



16 20 24 



TIME 



3i: 



Illumination 



2000 

 1000 

 500 



200 ■ 

 100 

 50 



20 

 10 

 5.0 



20 

 «I.O 



1 1 1 1 1 



0935 1520 2130 0335 0930 1520 2000 0330 0925 1525 



(B) 



24 4 8 t 12 16 20 24 4 4 8 12 16 20 24 4 8 12 16 20 24 4 8 12 16 



PHTR ^'•'E 



J I I ' 



c 



Illumination 



Fig. 2. Like Fig. 1, except that 420 ft-c of photoreactivating light was 

 applied 15 min after UV dose for 1 hr. 



was 50 ergs sec~^ mm~^, and the exposure times were zero, 90, and 

 120 sec. These operations were performed under dim red hght, and 

 UV exposures were completed by 1015. After irradiation the popula- 

 tions were retained in the dark or exposed to photoreactivating 

 (PHTR) light (420 ft-c, "dayhght" fluorescent illumination for 1 hr. 

 One milHliter aliquots of the twenty-four respective cell populations 

 were transferred under dim red light from the exposure vessels into 

 240 storage vials. These vials were placed in black envelopes within 

 copper cannisters suspended in a water bath held at 25 °C. The first 

 counts (24 vials, 3 on each graph) were made 71 hr after UV 

 exposure (0935), and counts were made at six hourly intervals for 

 three consecutive days until all ten sets of the vials were counted. The 



