( 66 ) 
II. With positions at an angle. 
Corresponding acceleration Presentation time 
sin 90°=^ XI 450' 
g X sin 60° = 0.866 g 600" 
g X sin 45° = 0.7071 g 690 ' 
g X sin 30° = 0.5 g 840" 
g X sin 15° = 0.259 g 1080" 
Product in ^-seconds 
450 
520 
488 
420 
280 
Froschel 1 ) considers that these figures prove the existence of the 
relationship in question; the number of values is however small, the 
variations are very large and are for small accelerations of such a 
nature that a more extensive and accurate investigation was considered 
desirable by Prof. Went 2 ). 
As Bach himself found, the presentation time for geotropic curvature 
depends very much on external conditions. The effective force cannot 
be varied within very wide limits (as in the case of light, where 
for instance a change from 1 to 140 million is possible). It is there¬ 
fore necessary to have a large number of experiments, and to make 
the experimental error small; these requirements need not be satisfied 
in the investigation of phototropic stimuli. 
I have therefore partially repeated Bach’s investigation in Prof. West's 
laboratory. As far as possible I took precautions to keep the external 
conditions constant. The experiments with plants placed at an angle 
were made in a perfectly dark space in the laboratory glass-house, 
in which the temperature was kept pretty constant at 24° C. In 
order to exclude phototropic curvatures, the observations were made 
with a red electric incandescent lamp. In order to eliminate individual 
differences, each experiment was done simultaneously with at least 
12 plants. I mostly used etiolated coleoptiles of Arena sativa ; before 
the beginning of each experiment very long and very short individuals 
were removed from the experimental box. The seedlings had germinated 
in the same glass-house in which they were used, so that the influence 
of changed conditions at the beginning of the experiment, observed 
by Bach, was also excluded. 
As a preliminary communication I here give a synopsis of the 
results of my experiments. 
? p f* 6SGHEL - a) ‘ U h) - Best err. bot. Zeit. Jahrg. 1909, no. 2. 
• F, C. Went, Proc. Roy. Acad, of Sciences. Amsterdam. Sept. 1908. 
