GEOTROPISM 125 



We suspect that this occurs through a change in mass 

 action in the nerve endings, in analogy to our experiments 

 on the influence of the mass of the leaf on the geotropic 

 curvature of Bryophyllum, but experimental data are 

 lacking. 



3. We observe phenomena of geotropism in animals 

 which have no ears, but this need not surprise us in view 

 of the observations on geotropism in plants, and in hy- 

 droids (Antennularia antennina). The writer 289 had 

 found that a holothurian (Cucumaria cucumis) has a ten- 

 dency to creep upward when put on a vertical object until 

 it reaches the highest level, where it remains. When put 

 on a vertical plate of glass or slate, these animals creep 

 untiringly upward if only the plate is turned 180 around 

 a horizontal axis as soon as they have reached the highest 

 point. It could be shown that light and oxygen supply 

 have nothing to do with the phenomenon. Jennings 

 observed that Paramcecia always gather at the highest 

 point of a vertical tube and that they assume this position 

 by active ciliary motion. Lyon 323 assumes that the body 

 of Paramcecia contains substances of different density 

 whose location is changed by changes in orientation of 

 the organism to the center of the earth and that these 

 changes automatically turn the animal again so that its 

 oral pole is directed upward. It will then continue to 

 swim in this direction. 



4. It is known since Knight's experiments that cen- 

 trifugal force can act like gravitation and we must assume 

 that the centrifugal force leads to an alteration in the 

 distribution of the sap or of other substances in the cell. 

 This leads to differences in the rate of chemical reactions 

 and may account for the phenomena of orientation under 

 the influence of centrifugal force. 



