122 



PHOTOCONTROL OF GROWTH 



It is interesting to compare the illustration of Meikoningin with that 

 of the variety requiring higher intensities, Wonder van Voorburg (Fig 

 7 ) . The difference between the two varieties is somewhat less obvious 

 in blue light than in yellow. Nevertheless it is clear that Wonder van 

 Voorburg at 26.000 ergs/cm- sec in yellow light is much more 

 elongated than the corresponding one in blue light, and also much 

 more elongated than the corresponding Meikoningin plant. 



50,000 26.000 10,000 



BLtJl LICST (0rg3/om2/s«o.) 



50.000 27.000 11 



rm.i.m i.tqh? ( ergs /m.'^ /sac . } 



Fig. 7. Lettuce, var. Wonder van Voorburg, grown in either exclusively 

 blue light or exclusively yellow light, both at three different intensities. 

 Photographed July 21, 1955. 



Bensink has cultivated a Meikoningin plant in blue light of 10,000 

 ergs/cm- sec which produces narrow leaves and considerable stem 

 elongation. This plant, upon being transferred to blue light of 50,000 

 ergs/ cm- sec, produced round leaves at its top, with short internodes. 

 This illustrates the possibility of direct reaction of young leaves to light 

 intensity. 



