170 KLINOSTAT. [CH. VII 



by the leaves -with the horizon should be noted, and 

 should again be measured after a few days. 



(217) The movements due to specific sensitiveness. 



It was at one time believed that the diaheliotropic 

 position was simply the result of a balance struck between 

 such opposing tendencies as apheliotropism, apogeotropism, 

 epinasty, &c. &c., and that diaheliotropism as a specific 

 form of sensitiveness was non-existent. This view has 

 now given way to the belief that a leaf in placing itself 

 at right angles to incident light is replying in a specific 

 manner to stimulation, just as a positively heliotropic 

 stem reacts in its specific way by placing itself parallel to 

 incident light. 



To illustrate this fact, plants must be subjected to 

 one-sided illumination while kept in slow rotation on the 

 klinostat. 



We use the instrument designed by Mr H. Darwin 

 and described by one of us' in the year 1880. 



The instrument is shown in fig. 34; the plant in a 

 flower-pot is fixed in a wooden box B, which again is 

 secured by the thumb-screw th to the Tplate pi: the box 

 being cubical can be fixed either as shown in the figure 

 or with the axis of the flower-pot at right angles to the 

 spindle (k) of the klinostat. The .plate pi is attached 

 to the spindle k which ends in a point turning in the 

 upper end of the left-hand support s. The spindle is 

 also supported at g on the friction wheel /r. The spindle 



' Francis Darwin, Linnean Society's Journal, Vol. xvin. p. 420. The 

 original klinostat is described by Sachs in his Arheiten, ii. p. 214. 



