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- 
tropic 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 th to the 
plate pl; 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 khnostat. The plate pl is 
attached to this spmdle, which ends ina point turnmg in the 
upper end of the left-hand support s. The spindle is also 
supported at g on the friction wheel fr. 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 R to the 
support s’. 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. 
