388 Sir J. C. Bose and Mr. G. Das. 



a surmise that the expansion of the opposite side, due to indirect stimulation, 

 was brought about by an induced increase of turgor. 



Fig. 12. — a, positive phototropic response and recovery from moderate stimulation ; 

 6, persistent positive curvature under stronger stimulation. {Dregea.) 



■ . JSsqpt. 11. — It would, undoubtedly, be a matter of great theoretical interest 

 if the induction of enhanced turgor on the distal side (by the action of 

 stimulus at the proximal side) could be demonstrated by some experiment of 

 a convincing character. I have explained elsewhere how enhanced turgor 

 brought about by increased internal hydrostatic pressure caused an erection 

 of the Mimosa leaf, a diminution of turgor causing its fall.* I now took a 

 Mimosa plant and applied a narrow circular beam of light from a small arc 

 lamp at a point on the stem diametrically opposite to the motile leaf which 

 was to serve as the indicator of induced variation of turgor under the uni- 

 lateral action of light. That the indirect stimulation caused an enhancement 

 of turgor of the opposite side was soon demonstrated by the erectile move- 

 ment of the leaf. This positive movement was initiated 20 seconds after the 

 application of stimulus, thus affording a proof, which appears conclusive, of 

 the induction of an increased turgor as the effect of indirect stimulation. 

 When the stimulation is moderate and of short duration, the response is only 

 positive. But when the stimulation is continued, the slow excitatory 

 impulse is conducted to the distal side with immediate fall of the leaf 

 (fig. 13). It was stated that conduction of excitation in a transverse direction 

 would prove very much slower than in the longitudinal direction. In the 

 present case the time taken for conduction across the stem 2 mm. in diameter 

 was 200 seconds, giving a velocity of -j-^p mm. per second. The velocity 



* ' Plant Eesponse,' p. 46. 



