CH. VIl] DECAPITATED ROOTS. 175 



is now fixed to a klinostat and kept in slow rotation in 

 damp air for 8 to 12 hours. The gravitation-stimulus 

 being removed by the use of the klinostat, the roots grow 

 freely into the glass tubes and are forced to assume their 

 form : thus each root has a sharp rectangular bend at 

 1'5 mm. from its tip. If the experiment has been properly 

 done the tubes should fit the roots so loosely that they can 

 be taken off and replaced with ease : this is said to be a 

 condition of success. 



The specimens having been removed from the cork 

 plate, they should be fixed (the tubes still attached) in 

 various positions. If the terminal To mm. is vertical and 

 the basal part of the root horizontal, no geotropic curve 

 occurs, although the root grows vigorously. The part of 

 the root within the horizontal limb of the tube is displaced 

 by the new growth within the tube and gradually emerges 

 from the tube. The fact that the growth of the root 

 continues horizontally seems only explicable by the 

 supposition that the tip of the root alone is geotropically 

 sensitive, and since this points vertically downwards it is 

 in a satisfied condition, without any tendency to curvature. 

 Other specimens should be fixed with the terminal 1*5 mm. 

 horizontal ; under these conditions the vertical portion of 

 the root outside the tube bends laterally until the tip of 

 the root is vertical. In this experiment the cotyledons 

 may be above, the main axis of the root pointing ver- 

 tically downwards, or vice versa, the root may be directed 

 upwards. For the different form of the subsequent 

 curvature in the two cases, Czapek's figs. 2 and 3 should 

 be consulted. 



