



390 VEGETABLE PHYSIOLOGY 



placed at an angle from the position which it usually assumes, 

 a curvature of the growing organ results, which lasts till the 

 normal attitude is regained. When, for instance, a young 

 seedling is detached from the earth and laid upon its side, 

 the stem gradually curves through an angle of 90 and 

 becomes erect, while the young root curves in the opposite 

 direction till it points vertically downwards. Similarly 

 when a runner is placed vertically, its apex is slowly de- 

 flected till it again grows parallel with the soil. These 

 movements are termed apogeotropic, geotropic, and diageo- 

 trdpic respectively. 



To prove these movements to be responses to the stimulus 

 of gravitation it is necessary to eliminate the action of the 

 latter force, and to observe the direction of growth under 

 the new conditions. This can be done by causing the plant 

 to grow supported upon an apparatus known as a Klinostat 

 (fig. 156). The plant, growing in a flower-pot, is fixed in a 

 wooden box B, which is secured by a thumb-screw ih to the 

 plate pi; the box is cubical in form, and can be fixed either 

 as shown in the figure, or with the axis of the pot at right 

 angles to the spindle k of the klinostat. The plate pi is 

 attached to this spindle, 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 jr. The spindle (with 

 the plant attached) is made to rotate by means of a band 

 of silk dr, passing round the wheel w, and also round a 

 pulley on one of the axles of an American watch-action 

 clock c, which is attached by means of the screw E to the 

 support '. By passing the driving-gear over the large 

 pulley W , the spindle is made to rotate once in twenty 

 minutes. By arranging wheels of different sizes at this 

 point, the period of rotation can be made longer or shorter. 



When the plant is placed in a horizontal position on the 

 revolving plate, every face of its axis comes successively 

 under the influence of gravity, so that all parts of it are 

 affected equally and similarly. No curvature of the hori- 

 zontal axis of the plant then occurs in any direction. 



