1 84 THE LIFE OF THE PLANT 



Thus the main direction of growth of root and stem 

 bears no permanent relation to light or moisture ; it is 

 only their position with regard to the horizon that is per- 

 manent : the root grows always downwards, the stem up- 

 wards ; in other words and speaking more strictly, since 

 this phenomenon is observed all over the globe, at the an- 

 tipodes as well as herewith us, the root is directed towards 

 the centre of the globe, and the stem away from it. This 

 very constancy of direction points to the fact that the 

 force to which it is due must be gravity, i.e. the attraction 

 of our planet. This can be proved by experiment. If this 

 direction of the parts of the plant depends upon the force 

 of gravity, then by eliminating its action, we shall arrest 

 the phenomenon itself ; by modifying the force we shall 

 modify the phenomenon also ; finally, by substituting 

 for this force another, which acts in a different direction, 

 we shall change the direction of the phenomenon 

 correspondingly. But how shall we actually do this ? 

 how can we remove any body on the surface of the 

 earth from the earth's attraction ? How can we 

 arrange matters so as to prevent the plant from having 

 a top and a bottom ? It is clear that we cannot do it 

 literally. We can, however, make gravity act at short 

 intervals in opposite directions and thus counterbalance 

 its own influence. For this purpose let us fix a germinat- 

 ing seed to the rim of a rotating wheel (e.g. a wheel set 

 in motion by electro-magnetic power). If the wheel 

 moves in a horizontal plane (as is shown in fig. 52, A i) 

 it will certainly not prevent the root from growing down- 

 wards and the stem upwards. But if the wheel moves in 

 a vertical plane (fig. 52, B i), or, what comes to the same 

 thing, if we fix the germinating seed to the minute hand 

 of a clock, it is clear that at every half-turn the position 

 of the root and stem will change ; in the end a top and a 

 bottom, a right hand and left hand side will cease to 

 exist for the seedling ; the continual action of the force 

 of gravity in any one direction will be prevented. 



