182 S. KLEIN 



TABLE I 



GERMINATION PERCENTAGES OF LETTUCE SEED 'PROGRESS' 



illuminated with Far Red for 2(FR2), SCFRa) and 7 days (FR-) and then 



transferred to darkness (D) or illuminated with red (250 ft.-c.) for 5(R5), 



20(R2o) or 40 seconds (R40) (Evenariio). 



The germination of the untreated seeds in darkness varies between 90-93% 

 (ref.io). 



Red reaction may not, after all, be responsible also for the 

 above mentioned phenomena. The case of the Progress seeds is 

 interesting also from another point of view. When these seeds 

 are imbibed in a solution of coumarin, they behave exactly like 

 the light-sensitive Grand Rapids variety!^. Thus, in cases in 

 which one does not normally find light sensitivity, under certain 

 conditions light may still have a profound influence. 



What makes understanding of the light mechanism still more 

 difficult is that blue light too, in many cases, has a distinct 

 influence, the nature of which is yet unclear. 



Without any doubt, however, the most important light 

 mechanism is the reversible 'short' Red-Far Red reaction. Until 

 very recently, attempts at identification of the pigment respon- 

 sible for this reaction were unsuccessful. A few months ago, the 

 photometrical detection of this pigment in living tissue of 

 maize shoots was reported by Butler, Morris, Siegelman and 

 Hendricks^''. The same group also succeeded in separating the 

 pigment from the tissue by methods of protein chemistry. A 

 spectral shift could be observed after both Red and Far Red 

 irradiation. This is a most important advance since it enables us 



