542 



RHYTHMS IN PLANTS AND ANIMALS 



2000 - 

 1000 

 500 



200 

 100 

 50 



20 

 10 

 50 







I 

 I 



I NORMAL 

 I REACTIVE 

 I PERIOD 



I 

 Dose (e*gs/fnm2) 



X 4500 



+ -. 6000 



UVi 



I. ..I 



0935 1520 2130 0335 0930 1520 2100 0330 0925 



X 



Illumination (mii 



0935 1520 2130 0335 0930 1520 2100 0330 0925 1525 



ILLUMINATION 



Fig. 1. The relationship between abihty of experimental paramecia to 

 mate, and the time of day at which the mixture with competent cells of 

 complementary mating type was made. Reaction magnitude of agglutina- 

 tion (RM) was measured 10 min after mixing. Four categories were 

 irradiated at each of four different phases during a reactive-nonreactive 

 diurnal cycle: A in the late scotophilic phase; B just before the middle of 

 the reactive phase; C at the end of the reactive phase; D just before the 

 middle of the scotophilic phase. 



Stock Wu-5, mating type D, in 250-ml Erlenmeyer flasks were trans- 

 ferred at the end of the exponential period of growth into four dif- 

 ferent light-dark compartments. The flask within each compartment 

 received 150 ft-c illumination from a 15-w daylight fluorescent lamp. 

 Each compartment was scheduled according to a photoperiodic cycle 

 consisting of 10 hr of Hght and 14 hr of darkness. From one compart- 

 ment to the next, each cycle was unique, with 6-hr spacings between 



