430 TRANSFORMATION OF ENERGY 



able centrifugal force was exerted which on its part affected the seedlings on 

 one side only. 



' I soon had the satisfaction of seeing,' writes Knight, 'that the roots, in 

 whatever direction they stood in reference to the position of the seed, turned 

 their apices outwards from the rim of the wheel and in later growth formed 

 nearly a right angle with the axle. The young stems on the other hand 

 grew in the opposite direction, and in a few days all their apices met in 

 the centre of the wheel.' 



In this experiment the seedlings are influenced by centrifugal force exactly 

 in the same way as they are by gravity when grown under natural conditions. 



In another experiment KNIGHT allowed gravity and centrifugal force 

 to act at the same time but in different directions. The seedlings were fastened 

 to a horizontally rotating disc and the distance of the plants from the centre 

 and the speed of rotation of the disc were so arranged that the mechanical 

 effect of gravity and of the centrifugal force were equal. Under such circum- 

 stances the roots grow outwards and downwards at angle of 45, while the 

 stem grew upwards and inwards at a similar angle. When the speed of 



Fig. 132. PFEFFER'S Klinostat, as manufactured by ALBRECHT of Tubingen. 



rotation was increased, the axes of the seedlings took up a position which 

 gradually approached the horizontal. From this it must be concluded that 

 the plant is unable to discriminate between centrifugal force and gravity and 

 that one force may be replaced by the other. Both forces have this in common, 

 however, that they act as accelerating forces on the plant body. 



Long afterwards, SACHS'S experiments (1874) added very important facts 

 to the fundamental data established by KNIGHT. In SACHS'S as in KNIGHT'S 

 first experiments the seedlings were made to revolve round a horizontal axis 

 but the speed of the revolution was very low, viz. about one revolution in 

 10-20 minutes. This speed indeed is so low that no centrifugal force worth 

 mentioning is produced ; since, however, the unilateral action of gravity is 

 eliminated owing to the continuous revolving movement of the disc, the roots and 

 shoots go on growing in the directions in which they were originally orientated. 

 By the employment of this apparatus, the curving (/cAiVctv) of the plant is 

 inhibited, so that SACHS (1879) termed it a Klinostat. Fig. 132 illustrates 

 such an apparatus in operation. The horizontal axis is driven by clockwork 

 and to this axis the plant is attached ; to the mechanical arrangements for 

 altering the speed of rotation we need not pay any attention. 



