A. U . (iALSTON AND RAILXDAR KAUR 



703 



Ihilike CiMl^ lenuron exerts its growth-promoting effect on etio- 

 lated sections only in the absence ol sucrose (Table 8) and at all 

 levels of lAA tested. 



E[ject of pliotoperlod of the pavent plant on groxi'tli characteristics 

 of green sections. Sections derived from 24-hour photoperiod plants 

 and supi^lied with sucrose grow better in the light and worse in the 

 dark than do sections from 8-hour and 16-hour plants (Fig. 17) . There- 

 fore, they may be considered as "light-adapted," in the sense that 

 etiolated sections are dark-adapted and are inhibited by very low 

 total irradiances of light (11). Similarly, sections from 8-hour photo- 

 period plants supj)lied with sucrose grow better in the dark and 

 worse in the light than do sections from 16- and 24-hour photoperiod 

 plants. Photoperiod is however, without effect on the sucrose optimum 

 (Fig. 18) or on the lAA optimum (Fig. 8) . 



Efject of morphogenetically active light. The growth of etiolated 

 sections is reversibly inhibited by weak red light (11), this inhibition 

 being dependent on the presence of sucrose (1) . Roughly a 50 per 

 cent inhibition of etiolated section growth can be induced by 50 



3 5 



3.0 



SUCROSE, LIGHT 



NO SUCROSE, LIGHT 



SUCROSE, DARK 



O NO SUCROSE, DARK 



Photoperiod (hours) 



Fig. 17. Effect of photoperiod of the parent plant on the growth of green 

 pea stem sections in light and dark. 



