( 345 ) 
It was now clearly shown, that a number of rootlets, which had 
curved geotropically, were completely free from starch. Whatever 
views we may adopt with regard to the harmful action of the 
aluminium on the plant, or with regard to the fact that by no means 
all roots were free from starch, the fact, established with certainty, 
that roots, the tip of which had become starch-free, nevertheless 
curved geotropically, proves conclusively that the perception of the 
stimulus of gravity can take place without statoliths. 
At most the protagonists of the statolith theory may still maintain, 
that the starch grains could in any case accelerate the perception of 
gravity. On this point a conclusive answer could only be obtained 
by determining, the presentation time for geotropism in roots with 
and without starch. This determination was unsuccessful, for two 
reasons : In the first place the harmfulness of the solution and the 
tendency to traumatotropic curvature make it necessary to stimulate 
somewhat longer in order to get curvatures which can be readily 
observed and secondly these water cultures cannot be placed on a 
clinostat during the latent period, a condition which is necessary in 
the case of this object, in order to obtain definite curvatures with 
the presentation time. 
Utrecht , October 1909. 
Physics. — “ The degree of completeness of the circular polarization 
of magnetically divided lines.” By Prof. P. Zeeman. 
1. A luminous gas placed between the poles of an electromagnet 
observed along the lines of force, gives in the simplest case, two spectral 
lines of different wavelengths. These lines are situated at both sides 
of the original line. In accordance with Lorentz’s elementary theory 
my observations so far published tend to show almost perfect pola¬ 
risation of the lines of this doublet, the polarization being right- 
handed for one, left-handed for the other of its components. If the 
direction of the field is reversed the sign of the polarization becomes 
opposite. 
Corresponding to the doublet, observed parallel to the field, a 
triplet is seen when the light emitted at right angles to the field is 
analysed. The components of this triplet are linearly polarized. 
Lorentz as early as 1898 ^ showed that some conclusions con¬ 
cerning the polarization of the components of magnetically divided 
*) Lorentz. These Proceedings June 1898. p. 113. The Theory of Electrons. 
Teubner. Leipzig, p. 149. 1909. 
