EFFECT OF LIGHT ON GERMINATION OF SEEDS 



93 



5 10 15 



Hours between Red and Infra-red Irradiation 



Fig. 4. The rate of escape of Grand Rapids lettuce seeds from control 

 by far-red radiation. Seeds irradiated 4 min with red after imbibition for 

 1 hr, and then after varying periods in the dark irradiated 16 min with 

 far red and returned to 2()°C in darlcness. 



With additional light exposure, however, germination takes place in 

 darkness at 20° (Toole et al., 1953). Also, some samples of lettuce 

 seed that originally germinate equally well in red light or darkness 

 are made sensitive to light by holding the imbibed seeds 3 or 4 days 

 at a temperature too high for germination (Table III) (Borthwick 

 etal., 1954). 



Table I. Germination of Seeds of Two Varieties of Lettuce 

 at Different Temperatures in Red Light and in Darkness 



