74 



RELATION OF PLANTS TO GRAVITATION 



horizontal position for 60 to 80 minutes. If placed in this posi- 

 tion for a less time, then revolved on a clinostat the relation of 

 the length of the reaction time to the duration of the stimulus 

 (exposition time) may be found. 



The rotation of an organ on its own axis, in a position in 

 which it receives geotropic stimulation presents all sides of the 

 sensory zone to the action of the stimulus, and thus brings the 

 organ into a state of tetanus so well balanced that no curvature 

 is shown. If gravity is replaced by centrifugal force, or rather, 



4b 



3h 



2h 



Us 



1234 6 8 10 15 20 25 30 35 40 

 Fig. 32. Curve showing relation of amount of centrifugal force and reaction time 

 of roots of Lupinus albus. Reaction times are denoted by the figures along the verti- 

 cal line, and amount of centrifugal force in terms of gravity along the horizontal line. 

 After Czapek. 



counteracted by it by being given in a different plane, an amount 

 of the centrifugal force amounting to but a thousandth of gravity 

 may be followed hy* a reaction after a period of six hours, and 

 when the centrifugal force is increased to 40 g. the reaction time 

 is shortened to 45 minutes. 



The angle of divergence from the normal geotonic position 

 of the organ exerts such effect that the maximum stimulus is re- 



