387 



A subsequent darkening caused the following reaction 



Here too the contrast between light- and dark-response is found. 

 Both are fairly equally niaiked. 



Meanwhile I have obseived the dark-growtli-response with an 

 ilhuninaiing-power of 512 M.K. I found as an average of 7 experi- 

 ments : 



Here we already approach the limit of the reactions still jiercept- 

 ible, which also appeared from the fact, that a few plants no more 

 gave a perceptible dark-growth-response. On subjecting these plants 

 to an illumination of 512 M.K., there did not occur a light-growth- 

 response either. 



The sensitiveness to light, found by Blaauw ("L. u. W. Ill") for 

 Sinapis alba was greater. Al the time there was even found a marked 

 response at 64 M.K. with a minimnm of 81 "/, and a rale of growth 

 after 2 hours of 91 7«. «■" equally strong response, as the one found 

 by us for 3500 M.K. To what causes this may be owing (older 

 seed? other Sinapis alba race?) should be further investigated into 

 and may become an indication for the deeper cause for sensitiveness 

 to light. 



The behaviour of the tap root of Avena Sntiva, with 

 respect to light and dark. 



Bi.AAUW did not find a perceptible response with illuminating- 

 powers of 64—500 M.K. I exposed to 3500 M.K. Even then no 

 reaction occurred, or so slight a reaction, that it might as well be 

 attributed to the slight rise of temperature. 



After a 3 hours exposure at a constant temperature of 20^° — 

 22^° C. followed darkening. In not a single case there was a marked 



