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resistance. At a certain distance from the lamp were placed boxes 
of Avena seedlings which were always put in such a position that 
their longitudinal axis made a small angle with the direction of the 
rays of light, so that the seedlings which to the number of 17 to 
20 stood in each box in one row, did not shade each other. For 
the geotropic stimulation the boxes were put upright on one of the 
narrow sides. For further details reference must be made to the 
fuller communication, which will appear later. 
The apparatus was placed in a part of the laboratory greenhouse 
at Utrecht fitted up as dark room, where arrangements for ventilation 
and warming make it possible to carry out experiments at constant 
temperature and in pure air. In this case the temperature was kept 
ata? °C. 
A series of experiments was generally carried out with six boxes. 
Nos. 1, 2, 3, and 4 were stimulated phototropically for six or ten 
seconds; No. 1 at a distance of 70 em. from the lamp, the other ones 
at one metre. The geotropic stimulation of boxes 3, 4, and 5 began 
50 minutes after the illumination and lasted 20 minutes (in some 
series 15 min.). Box 3 was placed upright in such a way that the 
side which during illumination had been in front, was now under- 
neath, whilst with box 4 the front of the illumination came upper- 
most; 6 had already been placed upright 20 (in other cases 15) 
minutes earlier and remained 40 (or 30) in this position. Two hours 
after illumination, i.e; 50 minutes after the end of the geotropic 
stimulation, the light as well as the gravitational curvature had 
reached its maximum; at that moment their magnitude was noted. 
For this I used a method recommended by LINDNER®, in which a 
lamp, placed at a sufficient distance, throws a shadow of the box 
on a strip of bromide paper, stretched immediately behind. This was 
later developed and preserved as protocol of the experiment. The 
horizontal deviation from the apex in mm. served as a measure of 
the curvature. 
In order to ascertain how far the average deviation of the 
17—20 seedlings in one box furnished a sufficiently reliable value, 
five boxes were stimulated in the same way phototropically and 
geotropically: first illuminated unilaterally for six seconds with an 
intensity of 10 M.C. and then 50 minutes afterwards placed upright 
and left for 20 minutes in this position. After 2*/, hours the devia- 
tions in m.m. amounted to: 
3.2, 3.2, 3.2, 3.3 and 3.3. 
1) P. Linpner, Ber. d.d. Bot. Ges. XXXII, 4. 1914. 
