;6 



RELATION OF PLANTS TO GRAVITATION 



Repeat with a seedling in a horizontal position so that the 

 axis will be at an angle of 90 with the horizontal. Repeat with 

 the root and hypocotyl only 45 ° from their normal vertical posi- 

 tion. Compare the data obtained in the set of three tests. 



113. Determination of the Presentation Time. Place a clino- 

 stat in position in a room with a temperature at about 20 C. and 

 adjust the extension axis in a horizontal position, and attach 

 a moist chamber. Fasten several seedlings in the chamber with 

 their axes in a horizontal position, and mark the exact position 

 of the apices of roots and shoots by means of additional pins 

 thrust in the cork plate to which they are attached. Allow the 

 apparatus to remain at rest for fifteen minutes, which will give 



Fig. 34.. Clinostat with moist chamber, containing seedlings, on extension arm. 

 After Giesenhagen. 



the roots and shoots a geotropic stimulus, but will not comprise 

 the full reaction time. Set the clinostat in motion at such rate 

 that it will make one revolution in ten minutes or slightly less. 

 After three hours stop the apparatus and note the position of the 

 apices in order to detect curvatures. Repeat the experiment, 

 allowing the seeds to remain at rest to receive the stimulus for 

 30 and again 50 minutes before setting the apparatus in mo- 

 tion. 



