426 



PLANT PHOTOPERIODISM 



TEMPERATURE COEFFICIENT 



The photoreaction for lettuce seed germination has been shown to 

 have a temperature coefficient of 1.0 as shown by Table I. Here the 



Table I. Photoreversibility of Lettuce Seed Germination 

 at Two Temperatures (Borthwick el al., 1954) 



importance is evident of separating the reaction from the confusion of 

 the assay, as permitted by reversal before the response gets significantly 

 under way. The implication of the upward creep in germination with 

 the number of cycles is indicated in Fig. 1. According to the tempera- 



Percent pigment conversion to for red 

 obsorbing form 



Fig. 1. A possible change in pigment conversion (schematic) and as- 

 sociated germination for several successive exposures to red (promotion) 

 and far-red (inhibition) radiations. 



