183 
illumination. We must conclude then that the latter can oceasion 
a retardation as well as an acceleration of the rate of growth. 
Most often we do not notice anything of the acceleration as it is 
concealed by the much more considerable retardation which is always 
present at the same time. Only when the value of the latter is the 
same on either side, a difference in acceleration will become visible 
in a curvature. 
If the above is correct, then it must also be possible to obtain an 
antiphototropie curvature with plants that have first been submitted 
to omnilateral fore-illumination. If this illumination is such that a 
further retardation of the growth cannot be obtained by a prolon- 
gation of the illumination, then an antiphototropie curvature must 
be obtained with a comparatively weak after-illumination. However, 
it should seem that thus far the exact strength of the fore-illumination 
has not been hit upon in similar experiments. Anyhow, the antitropic 
curvatures obtained were slight, and required moreover a rather 
intense after-illumination. 
In order to determine the retardation and the acceleration of the 
growth rate separately the processes should be severed. It is concei- 
vable that we have to do here with the influence of light on two 
different photo-sensible systems. As the sensibility of the two systems 
would not be equal in the different parts of the spectrum in this 
case, an analysis could perhaps be performed by using light of 
different colours. It is very well possible, however that there is only 
one photo-sensible system, and that it is not the light itself but a product 
originating as a result of the illumination, which exerts its influence 
upon two different systems. In that case the separation of the two 
processes might be rendered possible by a study of the influence of 
the external conditions. 
In connection with the last-mentioned supposition it is interesting 
to point out that according to the theory of Bose *) disturbances of 
equilibrium in the living organism manifest themselves in a contrac- 
tion, whieh is accompanied by an expansion in the adjoining tissue. 
The water expelled with contraction, would heighten the turgor of 
the adjoining tissue and thus occasion there a temporary quickening 
of the growth. In our case, then, the antiphototropic curvature of 
the tip might result from the occurrence of a normal curvature 
more downwards. The investigations of Arisz make it probable that 
under the conditions of our experiments normal curvatures may have 
1) J. G. Bose, Plant Response, Londen 1906; Life movements in plants. Vol. Il. 
Calcutta 1919. 
