232 



MOVEMENT IN PLANTS. 



(c) The labellum of Orchis is posterior, but by torsion 

 of the ovary during the unfolding of the bud it is brought 

 to the anterior position. That this torsion is induced by 

 gravitation is shown by the fact that if the plant is rotated 

 on a clinostat ( 306) the flower opens in the " inverted " 

 position. The torsion can also be prevented by the following 

 method. Cut off the flowering stem of Orchis, and bend 

 down the inflorescence so that it points vertically down- 

 wards : the young flowers do not undergo torsion. 



III. CLINOSTAT EXPERIMENTS. 



306. The Clinostat (or Klinostat), a most important 

 instrument in the study of geotropism and phototropism, 

 consists essentially of a driving mechanism which causes 

 the rotation of a rod (axis, or spindle) 

 carrying a plant-holder. In the simpler 

 forms the driving mechanism consists 

 of a clock, and the plant-holder is a 

 disk to which may be attached a small 

 pot or a wire cage, or some other ar- 

 rangement in which the plant is con- 

 tained or to which it can be fixed. The 

 rotating rod may be either placed hori- 

 zontally (plane of rotation vertical) or 

 vertically (plane of rotation horizontal), 

 or in an inclined position. The ordi- 

 nary form of clinostat gives continuous 

 rotation, but for some purposes an 

 intermittent clinostat is used. 



By means of the clinostat we can 

 eliminate the influence of either gravi- 

 tation or lateral illumination, or both, 

 thus preventing geotropic or heliotro- 

 pic curvatures. If the axis is vertical 

 (Fig. 52), the effect is to remove the 

 directive influence of light; if it is horizontal (Fig. 53), 

 the directive action of gravity is eliminated. In the 

 horizontal position, the clinostat may be used for both 



Fig. 52. Clinostat, in 

 vertical position as 

 used for experiments 

 on Phototropism. 



