iy Wis 
On comparison of the above experiments with those in tables 1 
aud 2, it at once follows that since in those of tables 3 and 4 there 
were curvatures, and not in those of tables 1 and 2, seedlings are 
unable to perceive a geotropic or phototropie stimulus in the absence 
of oxygen. 
The fact that the curvatures obtained in the later experiments are 
smaller than those obtainable under normal conditions proves, that 
the seedlings have undergone a harmful influence from the prolonged 
want of, oxygen, which still makes itself felt after the normal con- 
ditions have been reestablished. 
§ 4. The influence of oxygen deprivation on the reaction. 
In order to study the influence of an oxygen-free atmosphere on 
the reaction, | gave the seedlings a preliminary stay of 3 hours in 
nitrogen, administered the stimulus in this gas, and left them without 
oxygen also during the reaction time. The earlier experiments had 
shown that after a fore-period of 3 hours in nitrogen, the stimulus 
is still perceived normally in this gas. In a few experiments I watched 
the seedlings for a considerable further time in nitrogen in order to 
see whether a curvature occurred later. In that case we should have 
to postulate a lengthening of the reaction time owing to absence of 
oxygen. In the other experiments | admitted oxygen at once after 
the normal reaction time had elapsed, in order to see whether there 
was any after effect in this gas. 
1. Geotropic experiments. 
The plants remain the whole time in nitrogen. 
TABLE 5: 
Strength of stimulus 900 mgs. Temperature 20° C. 
| Time elapsed | ; | 
5 ‘ BLAS Number 
ee | Sagcunialadon: ee | Amount of curvatures ín mm. 
| in minutes | | 
| 
3 hours | 65 | i all without curvature 
| 100 | | id. 
125 | id. 
150 id. 
65 8 id 
100 id 
130 | id 
| 65 8 ‚7 without curvature, 1 with asymm. apex 
| 100 | id. 
| 130 | id. 
65 | i all without curvature 
19 
Proceedings Royal Acad. Amsterdam. Vol. XIX. 
