742 



PLANT RESPONSE 



now in one direction and again in the opposite, and whose 

 mystery lies mainly in this caprice. 



But the observer, in the course of his further inquiry, finds 

 that the vanes, whose rotation under the impact of the 

 external stimulus of wind first attracted his attention, are 

 but a part of a complex machine, the interior of which had 



been hidden from his view. 

 He finds that the energy 

 supplied from outside is 

 being transformed by a 

 dynamo inside, and stored 

 up in an accumulator. When 

 the external force is not 

 acting, the reverse move- 

 ment is caused by the 

 internal energy thus stored 

 up. This very movement, 

 being apparently without a 

 cause, he would formerly 

 have designated as auto- 

 matic. When the stored- 

 up energy is exhausted, 

 the seemingly autonomous 

 movement comes to a stand- 

 still, and only by the 

 accession of fresh external 

 stimulus, causing renewed 

 storage, can it be resumed. 

 At a given moment, more- 

 over, the responsive move- 

 ment of the vanes is determined by the opposing actions 

 of the external and internal factors. As long as the wind 

 is sufficiently strong, movement takes place in one direction, 

 and when there is a pause the internal energy begins to 

 find expression, by causing movement in the opposite 

 direction. If the circumstances were such that the rise of 

 the wind were synchronous with day, and its fall with night, 



Fig. 278. Diagrammatic Representa- 

 tion of a Windmill with Attached 

 Dynamo, D, and Accumulator, s 



Wind acting on vanes, v, from right, 

 represented by arrow {<-), causes 

 responsive rotation in direction 

 opposite to that taken by the hands 

 of a watch. This external energy 

 also causes electrical storage. On 

 the cessation of the wind the 

 accumulator begins to part with its 

 stored-up energy, and, the dynamo 

 now acting as a motor, causes a 

 responsive rotation of the vanes in 

 the other direction, as shown by the 

 arrow (■■>). 



