Researches on Growth and Movement in Plants. 



399 



or reversal. This may become accentuated by differential excitability of the 

 two sides of the organ. 



8. The normal effect undergoes modification when the tissue is in the 

 condition of sub-tonieity. The effect of stimulus on a sub-tonic pulvinus is 

 a positive mechanical or positive electrical response ; corresponding to this is 

 the positive variation or acceleration of growth in sub-tonic tissues, under 

 the stimulus of light or of electric shock. Continuous stimulation converts 

 abnormal positive to normal negative. 



9. Mechanical friction induces retardation of growth ; wounds cause a 

 more pronounced and persistent retardation. Unilateral stimulation of 

 contact brings about positive curvature in a tendril by the retardation of 

 growth at the proximal and acceleration at the opposite side. 



10. Electric stimulus induces retardation. Growth is affected by an 

 intensity of electric shock which is far below human perception ; the latent 

 period diminishes with increasing intensity of stimulus from 6 seconds to less 

 than a second. The incipient contraction under feeble stimulus culminates 

 under strong stimulus to a marked contraction of the growing organ. The 

 response of the growing organ is similar to the response of pulvinated organs. 

 In the polar action of electric current on growth, the anode is found to 

 enhance and the cathode to depress the normal rate. Unilateral stimula- 

 tion causes a positive electrotropic curvature. 



11. Light causes retardation of growth ; intense illumination arrests 

 growth ; but under long-continued exposure, growth may become renewed. 

 Unilateral application of increasing intensity causes a positive, dia-photo- 

 tropic, and reversed negative response. The more refrangible rays are the 

 more effective, the ultra-violet being most so. The thermal rays in the 

 infra-red are also effective. The phototropic curvature under sunlight is 

 partially due to the obscure radiation. 



12. These phototropic effects are accentuated in anisotropic organs where 

 one side is more excitable than the other. Tropic and nastic movements are 

 not distinct phenomena, but a continuity exists between the two. 



13. From the above it will appear that the generalisation has been 

 reached — that all the induced movements of plants under environmental 

 changes are the definite effects of direct and indirect stimulation. 



I take this opportunity to express my acknowledgment to Mr. P. C. Lyon, 

 C.S.I., the retired Minister in charge of Education to the Governpaent of 

 Bengal, for the facilities afforded to me and for his unremitting interest in 

 research. 



I also wish to offer my special thanks to the Eoyal Society which has not 



