AFTER-EFFECT OF LIGHT 75 



of stimulus of moderate intensity. Under a more intense 

 stimulation the incipient contraction does not end in the 

 arrest of growth, but the responding organ undergoes an 

 actual shortening of its length. 



Fig. 36. EfEects of continuous (a) electric and (b) photic stimu- 

 lation recorded on a moving plate (Crinum). 



Immediate and After-Effect of Light 



The Balance Method of observation offers, as previously 

 indicated, a unique opportunity of discovering the charac- 

 teristics of different responsive phases, both during the 

 exposure and after the cessation of light. I will describe 

 two illustrative examples with two different species of 

 plants, one of which was in a vigorous condition of growth, 

 while the other was in a slightly sub tonic condition. 



Experiment 41. Direct and after-effect of light. — The 

 specimen was a flower-stalk of Allium mounted on the 

 Balanced Crescograph. The index showed the normal 

 rate of growth to be 0-37 [x per second. After obtaining 

 the balance, the plant was subjected to light from a 

 small arc-lamp, being illuminated on all sides by suitably 

 inclined mirrors. The successive dots in the record are at 

 intervals of 10 seconds. The moment of incidence of light 

 is indicated by a vertical arrow, and cessation of light by 

 a horizontal arrow within a circle (see fig. 37). 



