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GEOTROPISM IN ANIMALS! 
I. GEOTROPIC CURVATURES IN ANIMALS 
As a continuation of observations which I have already 
published? I wish to give in the following pages some 
further facts which show that certain animals are compelled 
to orient their bodies in a definite way toward the center of 
the earth, as are certain plants. 
In order to show more clearly the similarity between the 
behavior of animals and that of plants in this respect, I 
quote the following passage from Sachs on geotropism in 
the plant kingdom: 
Whenever portions of a plant are moved by any cause whatso- 
ever from their habitual position into a different position with refer- 
ence to the horizontal, they bend until they again assume the same 
relation with the horizon which they had originally. This bending, 
which is brought about through the mere change in position, is the 
effect of a geotropic stimulus, the consequence of some property 
of the organs which does not give them any rest until they are 
again at their proper angle with the direction of the force of gravi- 
tation? 
These geotropic bendings of plants, as Sachs adds, “are 
brought about exclusively through growth, and only those 
organs which are still capable of growth can therefore regain 
their normal position with reference to the horizontal.” 
I have pointed out in an earlier paper that the roots of 
Aglaophenia pluma, a Hydroid, have the tendency to grow 
downward. Curvatures at the same time take place in this 
animal which are determined by internal causes, and which 
1Pfliigers Archiv, Vol. XLIX (1891), p. 175. 
2Sitzungsber. der Wiirzburger physik.-med. Gesellschaft, 1888, and Part I, pp.1 
and 89, 
3 J. Sacus, Vorlesungen tiber Pflanzen-Physiologie, 2d ed. (Leipzig, 1887), p. 717. 
176 
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