690 PLANT RESPONSE 



in the lateral leaflets of Destnodium gyrans % says they are in 

 no way disturbed by variation in the intensity of light. 

 According to Pfeffer, similarly, the autonomous movements 

 of the leaflets of Trifolium pratense are not affected by 

 illumination. But Strasburger again states that the leaflets 

 of this plant, on exposure to light, cease their oscilla- 

 tions. 



Investigations on the influence of light on the lateral 

 leaflet of Desmodium gyrans. — (a) In sub-tonic condition. — 

 A clearer insight into this subject will, however, be obtained 

 when I describe my experiments on Desmodium gyrans. I 

 have shown that when this plant is in a sub-tonic condition it 

 behaves like an ordinarily responding plant, such as Biopliy- 

 tum ; a single moderate stimulus then evokes a single response, 

 and strong stimulus multiple responses. Thus a leaflet of Des- 

 modium in a state of standstill has multiple response initiated 

 by the incident stimulus of light. The . following record 



FlG. 275. Initiation of Multiple Response in Lateral Leaflet of 

 Desmodium originally at Standstill 



Light applied at x and continued till the end of the sixth response, as 

 shown by the thick line. The responses show a staircase increase 

 with increase of absorbed energy. Pulsations persist for a short time 

 even on the cessation of stimulus. 



(fig. 275) shows this clearly. The leaflet was in a quiescent 

 condition, but during the application of light it exhibited 

 multiple responses, which, owing to the increasing absorption 

 of energy, showed a staircase enhancement of amplitude. On 

 the cessation of light the energy absorbed maintained the 

 pulsation for some time. 



(b) In normal tonic condition. — When the specimen, how- 

 ever, is in a favourable tonic condition, its pulsations being 



