( 1022 ) 
Botany. On the connection between stimulus and effect in photo- 
tropic curvatures of seedlings of Avena sativa. By W.H. Arisa. 
(Communicated by Prof. F. A. F. C. Went). 
At about the same time there appeared in 1908 papers by 
BraAuw 5) and by Fröscurr ®) on the perception of lightstimuh., 
If a seedling of Avena or Lepidium is unilaterally illuminated, 
then with different intensities of light a just perceptible reaction was 
found to take place, when the product of the intensity of light and 
the duration of the stimulus was a constant, 
A repetition of these investigations in Professor Went’s laboratory 
led to some observations of which L here give a preliminary account. 
Madame Porowzow *) showed for aerotropic and geotropic curva- 
tures, that under the microscope a curvature is seen to occur 
immediately after the stimulation.  BrLaavw') discusses to what 
extent this may also be regarded as probable in the case of photo- 
tropic curvatures. He is of opinion, that either the reaction where 
60 M 
Fig. 
Course of the phototropic curvature after BLAAUW. 
On the abscissa the time in minutes from the beginning 
of stimulation, on the ordinate the magnitude of the angle of deviation. 
it has beeome macroscopically visible must just have begun or 
that at this moment a new stage in the curvature process has 
been entered upon, and that therefore in any case he is working, 
with a definite point of the reaction. 
1) A. H. Braauw. Proc. Acad. Sci. Amsterdam, Sept. 1908. 
2) P. Fröscuer. Sitzungsberichte der K. Akad. der Wiss. Wien, April 1908. 
3) W. Porowzow. Untersuchungen über Reizerscheinungen bei den Pflanzen. 1909, 
4) A. H. Buaauw. Die Perzeption des lichtes. Recueil d. Trav. Bot, Néerl. Vol, 5. 
1909. 
