PHOTOCONTROL OF VEGETATIVE GROWTH 



133 



100 



. LJ Control 



T3 

 0) 



80 





60 



40 



en 



° 20 



c 



5 mm of For Red 



S 5 mm of For Red plus 5 mm of Red 



S 

 S 



Pinlo 



n 



Fig. 2. Effect of 5 min of far red or far red followed by 5 min of red on 

 internode lengths of beans, sunflower, and morning-glory when the irradia- 

 tions are made at the end of an 8-hr photoperiod of high-intensity fluores- 

 cent light. 



and far red. It seems to be caused by differences in subsequent reac- 

 tions initiated by the active form of the pigment. The linear relation 

 between response and duration of darkness fails for dark periods in 

 excess of 20 hr, indicating a dependence upon some other factor, possi- 

 bly some function of photosynthesis. 



MOOf 



20 





0^-^C 



For Red then Red 



J_ 



_L 



J- 



2 4 6 8 10 12 14 16 

 Hours of Darkness before Irradiation 



Fig. 3. Length of second internodes of Pinto bean plants in relation to 

 time within a 16-hr dark period at which length-promoting or length- 

 inhibiting treatments with radiant energy are given. Solid line, 5 min of 

 far red at time followed by 5 min of red at hour shown. Broken line, 5 

 min of far red at hour shown. 



