704 



LIGHT AND LIFE 



4.5r 



16 hr phofopd , light 

 24 hr photopd , light 



8 hr photopd , light 



16 hr photopd , dork 

 8 hr. photopd , dark 



24 hr. photopd., dork 



5 10 15 2 



Sucrose concentration (%) 



Fig. 18. Effect of the photopeiiod of the parent plant on the sucrose optimum 

 for growtii of green pea stem sections in light and dark. 



kiloerg.s/cm2 of red light (1) . All attempts to show any growth 

 inhibition of green sections by similar light treatments have been 

 unsuccessful. So far as we can determine, green sections are com- 

 pletely insensitive to photomorphogenic growth control by the red, 

 far-red system found in etiolated sections (11) and in intact green 

 plants (6). 



Conclusions 



These investigations have revealed important and extensive differ- 

 ences in growth characteristics to exist between green and etiolated 

 pea stem sections. From the point of view of photobiology, the most 

 interesting differences are the following: 



(i) Etiolated sections are markedly inhibited by low irradiances 

 with red light, while green sections are not. 



(ii) Etiolated sections are markedly promoted by cobaltous ion, 

 while green sections are essentially not. 



