234 MOVEMENT IN PLANTS. 



309. Elimination of Geotropism in Boots. To one 



side of a flat circular cork (J.) fix several Bean or Pea 

 seedlings in different positions, with two pins through 

 each seed to keep it in place ; between the seeds pin to the 

 cork pieces of wet cotton- wool, some of which project 

 beyond the margin of the cork. Prepare a second cork 

 (B) in the same way, with the same number of seedlings 

 fixed in as nearly as possible the same positions. With 

 the clinostat axis horizontal, fasten A to the holder so that 

 it is vertical ; set a dish of water below, so that the pro- 

 jecting bits of cotton- wool will dip into the water as the 

 cork revolves. Set the cork B vertical so that it also dips 

 into water; some at least of the radicles should lie 

 horizontally. 



After a day or two, note that the radicles of the seed- 

 lings on the fixed cork are growing downwards, curving 

 where necessary to do this ; but the radicles of the seed- 

 lings on the clinostat simply grow straight on and under- 

 go no curvature, so that they still point in different 

 directions. 



31O. Elimination of Geotropism and Phototro- 

 pism. Place the clinostat so that the axis is parallel to the 

 plane of the window, and fix a pot of seedlings horizontally 

 to the holder. After a day or two note that the shoots do 

 not curve, but grow quite straight in this position the 

 effects of both gravitation and light on the shoots are 

 eliminated. 



311. " Rectipetality." Fix a pot of darkness-grown seedlings 

 to the clinostat, placed horizontally and set in a dark chamber. 

 Do not start the clock until the seedlings have remained horizontal 

 long enough to show a distinct apogeotropic curvature ; then start 

 it, and after a day or so note that the curvature has disappeared 

 owing to autotropism (rectipetality). 



312. Reaction Time and Presentation Time. The time 

 during which a root or shoot must be kept horizontal until bending 

 begins is called the (geotropic) reaction time ; determine this for 

 the radicles and shoots of several seedlings in the Bean radicle it 

 is about 80 minutes. 



