76 CHAP. VIII. EFFECT OF LIGHT ON GROWTH 



The record shows that the balance, after a latent period 

 of 40 seconds, was upset upwards, indicative of retardation 

 of growth. The total duration of application of light was 

 about 5 minutes ; the retardation persisted for a further 

 period of a minute and a half. After this the rate of 

 growth became normal for about 2 minutes, as seen in the 

 approximately horizontal record at the top of the curve, 



Fig. 37. Direct and after-effect of light recorded by Method 



of Balance (Allium), 



characterised by two small pulsations. The most interesting 

 after-effect of stimulation by light was then exhibited in the 

 down-curve, indicative of enhancement of the rate of growth 

 above the normal, which persisted for 8 minutes. After 

 this, the growth-rate was restored to normal as indicated 

 by the horizontal record (fig. 37). 



Experiment 42. Effect on a slightly suhtonic specimen. — 

 A seedhng of Wheat was mounted on the Balanced Cresco- 

 graph and record was first taken under exact balance, 

 giving a horizontal line. Light from the arc-lamp was 

 now apphed for a few minutes. The record shows, by the 



