176 LIFE AND WORK OF SIR JAGADIS C. BOSE 



thought that they are unable to perceive a stimulus 

 unless applied for a considerable length of time. Thus for 

 the perception of geotropic stimulus it is supposed that 

 ' even in rapidly reacting organs there is always an interval 

 of about one to one and a half hours, before the horizon- 

 tally placed organ shows a noticeable curvature, and this 

 latent period may in other cases be extended to several 

 hours (Jost).' Bose finds that the latent period of geo- 

 tropic perception is often as short as a second. 



As regards perception of light, it has been supposed 

 that the period of effective exposure must at least be of 

 seven minutes' duration. With his extraordinarily sensitive 

 apparatus Bose investigated the question of the plant's 

 capability to respond to stimulus of light of excessively 

 short duration. We can hardly conceive of anything so 

 fleeting as a single flash of lightning. Bose now subjected a 

 growing plant, balanced in his Crescograph, to an artificial 

 flash of lightning that is to say, to the light emitted. by a 

 single electric spark between two metallic balls. The plant 

 perceived this light of incredibly short duration, as was 

 manifest from the upset of the balance, and the resulting 

 automatic script made by the plant. 



So much as regards the perception of plants to minimum 

 duration of stimulus. The next question is as regards their 

 range of perception, and Bose's astonishing discovery of 

 the response of plants to wireless stimulation has caused 

 something like a sensation among the scientific public. 

 The account of this discovery is best told in Bose's own 

 words taken from the second volume of the ' Transactions ' 

 of his Institute, and from his letter in Nature : 



A growing plant bends towards light ; this is true, not only 

 of the main stem, but also of its branches and attached leaves 

 and leaflets, This movement in response is described as the 

 tropic effect of light. Growth itself is modified by the action 

 of light : two different effects depending on the intensity are 

 produced ; strong stimulus of light causes a diminution of rate 

 of growth, but very feeble stimulus induces an acceleration of 



