594 LIFE MOVEMENTS IN PLANTS 



after which neutralisation set in, and by 4 p.m. the positive 

 phototropic effect had become partially neutralised. Arti- 



FiG. 217. — ElTect of periodic alternation of light L, and of darkness D, on 

 the response of ihimosa leaf. The |irst darkness causes the pre-masimal after- 

 effect of slight erection followed by recovery. The subsequent application of 

 light from 2 to 4 p.m. caused erectile movement followed by partial neutralisation 

 by 4 p.m. Stoppage of light at the third thick dot caused a sudden fall of 

 leaf below the position of equilibrium. 



ficial darkness at the third* thick dot caused a rapid down- 

 movement which overshot the position of equilibrium. 

 The difference of after-effect in the forenoon and in . the 

 afternoon lies in the fact that in the first case it was the 

 pre-maximum after-effect ;, but in the second case the 

 after-effect was post-maximum. I have already shown in 

 the previous chapter that the pre-maximum after-effect of 

 light is a short-lived movement in the same direction as 

 under light, while post-maximum after-effect was a rapid 

 over-shooting downwards beyond the equilibrium posi- 

 tion. These characteristics are also found in the after- 

 effects of light in Mimosa. 



