CH. VII] KLINOSTAT. 191 



(217 A) Exclusion of both heliotropic and geotropic 

 curvature. 



If the klinostat is arranged so that the spindle is 

 parallel to the plane of the window, heliotropic as well as 

 geotropic effects are avoided. This may be simply shown 

 by keeping a pot of seedlings rotating for a day or 

 two, and observing that they do not curve but remain 

 straight. 



(218) Rectipetality. 



A pot of young mustard seedlings (Sinapis) which 

 have been grown in the dark is placed on a klinostat 

 placed in a darkened room. The clock is stopped and 

 the plants allowed to remain in one position in the dark, 

 until a measurable geotropic curvature is produced. The 

 clock is then set in motion and after 24 to 36 hours 

 the curvature is found to be greatly diminished or to have 

 quite disappeared. This automatic recovery from growth- 

 curvature has been named rectipetality by Vochting 1 . 



(219) Mode of action of the klinostat. 



Two views are possible as to the mode of action of the 

 klinostat. It might be supposed that the plant does not 

 curve geotropically (or heliotropically as the case may be) 

 because it never has time to perceive the stimuli. Or, it 

 might be supposed that the stimulus is perceived but 



1 Die Beweyungen der Bliithen und Frtichte, 1882. 



