74 



CHAP. VIII. EFFECT OF LIGHT ON GROWTH 



have been sufficient, but would have required a very long 

 exposure. The intensity was increased by bringing the 



lamp nearer the plant ; marks were made 

 on a horizontal scale so that the intensity 

 of incident light increased at the succes- 

 sive marks of the scale as 1:2:3, and 

 so on. The duration of exposure was 

 the same in all cases, namely, 5 minutes. 

 After each exposure to light, suitable 

 periods of rest were allowed for the 

 plant to recover its normal rate of 

 growth. The records in fig. 35 show in- 

 creasing retardation induced by stronger 

 intensities of light. Table IX gives the 

 result obtained with another specimen. 



Fig. 35. Effect of 

 light of increasing 

 intensity in retar- 

 dation of growth. 



First record normal ; 

 second and third 

 records under in- 

 tensities of 2 and 

 3 units (Crinum). 



Effect of Continuous Light 



Experiment 40. — The effect of con- 

 tinued light of moderate intensity in 

 bringing about increasing retardation of 

 growth will be seen in fig. 36, h, side by 

 side with the record of effect of con- 

 tinuous electric stimulation of constant intensity on growth 

 (fig. 36, a). In both cases the effect of continuous stimula- 

 tion is seen to be essentially similar, namely, iricreasing 

 retardation culminating in arrest of growth. This is true 



Table IX. — Effect of Light of Increasing Intensity on 

 THE Rate of Growth (Crinum). 



