MOVEMENTS OF PLANTS 



39 



position, inasmuch as it is not vertical, originates a 

 new stimulus, and the new curvature which follows 

 brings the shoot back towards the upright position. 

 It may again overshoot the mark, but b}^ repeated 

 corrections it finally attains the normal upright 

 posture. 



It is this power of correcting the line of growth 

 whenever it deviates from the upright that enables 

 the pine tree to grow straight upwards. And this 

 is what I meant when I said that its habit of 

 growth depends on regulated curvature, to which no 

 one can refuse the name of movement. 



The pine and the seedling have, in fact, a 

 wonderful kind of sensitiveness — a sensitiveness to 



T^P* 



35or*> 



2 30^ 



Fig. 2. — A Valerian stem curving geotropically. 



the force of gravity. To those accustomed to think 

 of Mimosa as the sensitive plant par excellence my 

 words may sound strange. But the sensitiveness 

 of Mimosa is crude by comparison with that of the 

 seedling. A plant with a perception of the position 

 of the centre of the earth and a power of growing 



