



Figure 7-4 

 Reversal of lettuce seed germination with red and far-red light. Legends 

 under individual lots indicate sequence and number of red and far-red 

 treatments. Red irradiations were for 1 min and far-red irradiations for 

 4 min. If the last exposure is to red, seeds germinate; if to far-red, they 

 remain dormant. Temperature during the half hour required to com- 

 plete the treatments was 7 C. During all other times temperature was 

 19 C. Photograph furnished by Harry Borthwick, Agricultural Research 

 Service, Plant Industry Station, United States Department of Agricul- 

 ture, Beltsville, Maryland. 



