EFFECT OF LIGHT ON GERMINATION OF SEEDS 



97 



exposure to the high temperature. If the high temperature comes after 

 the irradiation, 8 times as much energy is required for promotion of 

 50% germination as is required if the high temperature precedes the 

 irradiation. The short period at the high temperature changes the 

 sensitivity of the photoreaction. For inhibition by far red, the energy 

 requirement was shghtly less if the high temperature came after rather 

 than before irradiation. In all instances when the sensitivity to red light 

 increased, the sensitivity to far-red radiation decreased, and the 

 reverse. 



Interaction between light and temperature occurs in the germina- 

 tion of other seeds. Seeds of Finns virgimana respond to exposure to 

 red light when held at 25 °C, but not when held at 20° or 30° (Toole 

 et al., 1956). Here also some block in the germination process pre- 

 vents complete response to the photoreaction at 25° (Fig. 5). If 



Light 



Dark 



to 25°C 



Fig. 6. Germination responses of seeds of Pinus viiginiana to red light 

 as influenced by temperature change. 



