1286 
the unilateral opposition of gravity, curvatures arise in a contrary 
direction in plants previously illuminated omnilaterally. 
These experiments can be simplified by illuminating the seedlings 
from above instead of making them perform a certain number of 
revolutions during illumination. This has been done in all subsequent 
experiments. The quantity of light is again given in M.C.S. ; in con- 
nection with this it should be remembered that it of course makes 
a difference to the plant whether the uppermost part of the apex 
only is constantly exposed to the light or whether successively the 
whole surface. Further, another sort of incandescent lamp was used 
in these experiments. 
Geotropic stimulation lasted 380 minutes. After this removal to 
the clinostat. Examination 3’/, hours after the completion of stimulation. 
Duration of Strength of Product MCS 
illumination illumination | Curvature 
16 min. SME: wl 4000 ke 
4 „ 8 MC 1000 ek 
ier 8 MC 250 + 0.7 
15 sec. 8 MC 60 | Eel 3 
= — — EEK: 
In other experiments the duration of the geotropic stimulation was _ 
changed, e. g.: 
Time of illumination 20 min., strength 8 M.C., product 5000 M.C.S. 
Horizontal during 
40 min. 20 min. 10 min 5 min. 
_ 
| 
| 
—09  —25  — 2,0 | — 1.8 (3 hoars on the cli« 
nostat). 
As is seen, the result is only slightly dependent on the duration 
of the geotropic stimulation. 
The fact that in 40 min. a great deviation is observed, is undoubt- 
edly connected with the fairly rapid cessation of the influence of 
preliminary illumination. When half-an-hour is allowed to elapse 
between illumination and geotropic stimulation, the influence of the 
first factor can no longer be demonstrated with certainty. This 
result is in remarkable agreement with the rapid disappearance of the 
