ae 5 4 3 
yt nen Pe aha ESES 
I |] 2.6 | 0.8 | 3663.4) = 
Bal 10 Manet le pie 1.0 (1.5) 
io) Bier Laren MA oe 
v | 25 | 1.7 | 3.142) 0.5 (0.8) 
Vel 5D) LIN DLD 
vi | 21 | 1.2 | 3.433) 1.2 (0.9) 
vit | 1.4 | 1.2 | 2.6(@.6) | —0.2 (0.2) 
| 
This complete ‘summation is all the more remarkable when the 
figures are compared with those of the illumination with the double 
amount of energy. These remain everywhere behind the summation 
curvatures. We find here a confirmation of the surmise that the 
phototropie curvature does not remain below a certain maximum 
in consequence of increased mechanical resistance, but that in reality 
under the influence of the illumination there occurs a change of 
condition in the plant, whereby the phototropic curvature with increase 
of the stimulus finally again diminishes and may even attain negative 
values, as Crark') and Arisz*) have shown for Avena. 
If the gravitational stimulus is applied immediately after illumi- 
nation, then the geotropic curvature has almost completely dis- 
appeared when the phototropic one reaches its maximum. A single 
example will suffice to show this. 
Deviations in mm. 2'/, hours after the beginning of the experiment: 
1.6 (40) 1.3(40 -20min.) 1.9(40-++20 min.) ae: min.) 
The maximal geotropie curvature 50 minutes after the cessation 
of stimulation amounted in this case to about 1.5 mm. The small 
deviation which still remains after 2'/, hours, shows itself clearly 
however in the figures of 3 and 4. 
In some experimental series the boxes were placed on the clinostat 
before and after stimulation in order to eliminate the opposing 
1) O. L. Crark. Uber negativen Phototropismus bei Avena sativa. Zeitschr. f. 
Bot. V. 1913. 
2) W. H. Arisz. Proceedings K. Akad. v. Wet. Amsterdam. October 1913. 
