EFFECT OF LIGHT ON GERMINATION OF SEEDS 95 



Table IV. Germination of Seeds of Lepidiiim virginicum with Different 



Temperature Treatments" 



Seeds Germinating, % 



Temperature, °C, Temperature, °C, 



First 2 Days After 2 Days 



15 15 



25 25 



25 IS 



15 25 



° Seeds irradiated with red at end of 2 daj's. 



block was removed and more of the seeds could respond to the photo- 

 stimulation if a suitable temperature change was made at the time of 

 irradiation. 



Germination of seeds of Lepidium virginicum is also increased by 

 a short period at a high temperature (35°C) at or near the time of 

 irradiation (Toole et ai, 1955b). When Lepidium seeds are imbibed 

 in the dark at 20° for 24 hr, given a saturating irradiation with red 

 light either just before or just after a 2-hr exposure to a temperature 

 of 35° and then returned to 20° for about 4 days, germination is 

 practically complete (Table V). The energy of irradiation required 

 for a germination of 50% is greatly influenced by the timing of the 



Table V. Germination of Seeds of Lepidium virginicum Irradiated Just before or 



Just after Being Held for 2 hr at 35°C« 



Duration of Irradiation, sec Seeds Germinating When Irradiated, % 



" Seeds imbibed in water at 20° for 24 hr l)efore placing at 35°; returned to 20° after 

 treatments. 



* Duration 64 and 16 min, respectively, for lots irradiated before and after 2-hr period 

 at 35°C. Germination 0, 27, and 55%, respectively, for seeds held continuously at 20°C in 

 the dark or with prior 4 or 64 min of red. 



