220 Prof. Bose and Mr. Das. Physiological Investigations with 



rendered insensitive for nearly an hour, the excitability is then gradually 

 restored almost to its normal value before operation. Under constant 

 external conditions, this excitability remains practically constant for about 

 24 hours, after which depression sets in. The rate of fall of excitability 

 becomes very rapid 40 hours after the operation, being finally abolished 

 after the fiftieth hour. The most important outcome of this inquiry is the 

 demonstration of the possibility of obtaining persistent and uniform sensi- 

 bility in isolated preparations. On account of this, not only is the difficulty 

 of supply of material entirely removed but a very high degree of accuracy 

 secured for the investigation itself. 



4. Effect of Amputation of Upper Half of Pulvinus. 



The determination of the role played by different parts of the pulvinus in 

 response and recovery is of much theoretical importance. Our knowledge 

 on this subject is unfortunately very scanty. The generally accepted view 

 is that on excitation "the actual downward curvature of the pulvinus is 

 partly due to a contraction of the walls of the motor cells consequent upon 

 the decrease of turgor, but is accentuated by expansion of the insensitive 

 adaxial half of the pulvinus — which was strongly compressed in the unstimu- 

 lated condition of the organ — and also by the weight of the leaf."* According 

 to Pfeffer, after excitation of the organ, "the original condition of turgor is 

 gradually reproduced in the lower half of the pulvinus, which expands, 

 raising the leaf and producing compression of the upper half of the pulvinus, 

 which aids in the rapid curvature of the stimulated pulvinus."f 



Fig. 4. — Effect of amputation of upper half of pulvinus. (1) Normal response before 

 amputation ; (2) response after amputation (Successive dots at intervals of O'l sec). 

 Apex-time 1 - 1 sec, in both. 



It was held, then, that the rapidity of the fall of leaf under stimulus is 

 materially aided (1) by the expansion of the upper half of the pulvinus, which 



* Haberlandt, ' Physiological Plant Anatomy,' 1914, p. 570, English Translation, 

 Macmillan & Co. 



t Pfeffer, ' Physiology of Plants,' vol. 2, p. 75, English Translation, Clarendon Press. 



