784 



The curvature is thus seen to occur with a very small quantity 

 of light (2^2 to 10 metre-candle-seconds) and these curvatures, which 

 already appear after 5 — 7 min. and are mostly weak, have not been 

 noticed by me before. Formerly I found a curvature only with the 

 most sensitive specimens, for example, after 50 metre-candle-seconds. 

 That was the curvature discussed above which occurs, when the 

 acceleration of growth has already passed off and of which the 

 reaction-time (observations being made with a telescope) amounts to 

 8 — 15 min. at least. We see therefore, that as a necessary result of 

 the photo-growth-reaction and the refraction of light, weaker curva- 

 tures also occur with still less illumination and these of necessity 

 have a rather shorter reaclion-time. 



Whilst then these small curvatures are visible with 27^ to 10 

 Metre-candle-seconds in proof of a liminal local acceleration of the 

 stretching of the cell wall, there occurs with a slightly stronger 

 illumination or with the same illumination in "more sensitive" 

 specimens — a reaction, which also could have been anticipated. 

 In such cases, as those of table VII the quantity of light is just 



