this mixture and allowing perception also to take place in it, and 
then letting any possible reaction occur in ordinary air. 
1. Geotropic experiments. 
PAB LEA 
Strength of stimulus 900 mgr. Temperature 20° C. Reaction time 65 minutes 
Fore-period in Number of | 7 
43 rH oxygen. seedlings. | Amount of curvature in mm. 
6 hours 9 OEE Be Re OTE ET 
| 
ans 9 3 IE ke (DES 2A PI 97 
ve eee 8 
EE (ct ne i (en ales Meee A ae 8 
2. Phototropic experiments. 
TABLES: 
Strength of stimulus 40 M. C.S. Temperature 20° C. Reaction time 75 minutes. 
Fore-period in Number of 
4.3 %) oxygen. | seedlings. Amount of curvature in mm. 
10 hours 9 Di, Dern EE De AM Lille, AML rae 
24 > 9 Ne STI Le TAN OD At Pe 
After a stay of 24 hours in the mixture of nitrogen and oxygen 
an. influence on the perception is noticeable in both cases. The 
seedlings therefore remain able for a long time to perceive a 
geotropie or phototropic stimulus in an atmosphere containing a 
relatively low amount of oxygen. Here also there is no indication 
of a difference in the reaction to these two kinds of stimuli, contrary 
therefore to the opinion of Correns, according to which a geotropic 
curvature can be executed in a lower percentage of oxygen than 
a phototropic one. 
Utrecht, February 1917. 
JI 
