1172 
2. Phototropic experiments. 
The seedlings remain the whole time in nitrogen. 
TABLE: 
Strength of stimulus 40 M. C. S. Temperature 20° C. 
| Time elapsed 
Haars bs | singe Dearne | ee Amount of curvature in mm. 
| in minutes (ae 
3 hours 15 1 ‚all without curvature 
| "100 | id. 
| 140 | id. 
| 170 | id. 
| 75 8 id. 
| 105 | id. 
| 130 | id. 
| 15 hee id. 
| 100 id. 
| 13D =o | id. 
| 75 Ë 9 id. 
If I replaced the nitrogen by air after 65 minutes, or respectively 
after 75 minutes there was always a slight after effect, which was 
plainly visible abont one hour after air bad begun to be sucked 
through. This is further evidence, that the stimulus had indeed been 
perceived, but that without oxygen no reaction could show itself. 
That these curvatures were so slight, is a proof that the stimulus 
was already passing off, and therefore we cannot speak of a length- 
ening of the reaction time as a result of the absence of oxygen. 
These experiments show, that a perceived geotropic or phototropic 
stimulus is unable to give a reaction in the absence of oxygen; 
further that there are no indications in favour of a lengthening 
of the reaction time. 
§ 5. Influence of an atmosphere with low oxygen content. 
By passing the gas from the nitrogen cylinder straight into the 
thermostat, without passing it first through the washing bottles with 
pyrogallol and the tube with red-hot copper, the plants were in an 
atmosphere containng 4—5 °/, of oxygen. I only investigated the 
influence on the perception, by giving the seedlings a fore-period in 
