CHAPTER XVII 



RESPONSE OF PLANTS TO WIRELESS STLMULATION 



A GROWING plant bends towards the light, and this is true 

 not only of the main stem but also of its branches and 

 the attached leaves and leaflets. It has already been shown 

 how light affects growth, the effect being modified by the 

 intensity of radiation. Strong stimulus of light causes re- 

 tardation of the rate of growth, but a very feeble stimulus 

 induces acceleration. The tropic effect is very strong 

 in the more refrangible region of the spectrum with its 

 extremely short wave-length, but the effect declines 

 practically to zero towards the less refrangible rays — the 

 yellow and the red. Proceeding beyond the infra-red 

 region, there comes the vast range of electric radiation, the 

 wave-lengths of which vary from o-6 cm., the shortest 

 wave I have been able to produce, to others which may be 

 miles in length. There thus arises the very interesting 

 question whether plants respond to the long ether waves, 

 including those employed in signalling through space. 



At first sight this would appear to be very unlikely, 

 for the rays known to be the most effective are in the blue- 

 violet region with wave-length as short as 30 x lo"^ cm., 

 whilst the electric waves used in wireless signalling are 50 

 million times as long. The perceptive power of the human 

 retina is confined within the very narrow range of a single 

 octave, the wave-lengths of which lie between 70 x io~^ cm. 

 and 35 X io~^ cm. It is difficult to imagine that plants 

 could respond to radiations so widely separated from each 

 other as those of visible light and those of invisible electric 

 waves. 



