V 



GEOTROPISM IN ANIMALS 1 



I. GEOTROPIC CURVATURES IN ANIMALS 



As A continuation of observations which I have already 

 published 2 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, T 

 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. 3 



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 



iPflilgers Archiv, Vol. XLIX (1891), p. 175. 



iSitzungsber. der Wilrzburger physik.-med. Gesellschaft, 1888, and Part I, pp. 1 

 and 89. 



3 J. SACHS, Vorlesungen ilber Pflanzen-Physiologie, 2d ed. (Leipzig, 1887), p. 717. 



176 



