CHAPTER XVII 



THERMOTROPISM 



Under the name of thermotropism M. Mendels- 

 sohn 35 -- 3:i;i has described the observation that ParamcBcia 

 gather at a definite end of a trough when these ends have 

 a different temperature. The organisms were put into a 

 flat trough resting on tubes through which water was 

 flowing. When the water in the tube had a temperature 

 of 38° at one end of the trough, while the tube at the 

 opposite end was perfused by water of 26° the organisms 

 all gathered at the latter end. If then the temperature 

 of the water in the two tubes was reversed the organisms 

 went to the other end of the trough. If one end had the 

 temperature of 10° the other of 25°, all went to the latter 

 end. In this case we are in all probability not dealing with 

 a tropistic reaction but w T ith a collection of organisms due 

 to the mechanism of motion described for Paramecium 

 by Jennings. When these organisms come suddenly from 

 a region of a moderate temperature to one of lower tem- 

 perature the activity of their cilia is transitorily reversed, 

 but owing to the asymmetrical arrangement of their cilia 

 they do not go back in the old direction but deviate to one 

 side. This can lead to a collection of Paramcecia such as 

 Mendelssohn described. 



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