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



contraction, and the response is, therefore, the lifting of the petiole. Thus, 

 in an intact specimen, excitation causes antagonistic reactions of the two 

 halves. But the sensibility of the upper half is very feeble and the rate of 

 its contractile movement, relatively speaking, very slow. The record of the 

 response of the upper half of the pulvinus, seen in fig. 5, was taken with an 

 oscillating recorder, where the successive dots are at intervals of 1 sec. : 



Fig. 5. — Response after amputation of lower half of pulvinus. (Successive dots at 

 intervals of a second ; vertical lines mark minutes.) Apex-time, 40 sees. 



the magnification employed was about five times greater than in recording 

 the response of the lower half (fig. 4). The intensity of stimulus to evoke 

 response had also to be considerably increased. Taking into account the 

 factors of magnification and the intensity of stimulus for effective response, 

 the lower half I find to be 80 times more sensitive than the upper. Thus, 

 under feeble stimulus the upper half exerts practically no antagonistic 

 reaction. The excitatory response of the upper half is also seen to be very 

 sluggish. 



6. Influence, of the Weight of Leaf on Rapidity of Responsive Fall. 



It is obvious that the mechanical moment exerted by the weight of the 

 leaf must help its responsive fall under excitation. But the relative import- 

 ance of the factors of active contraction of the lower half of the pulvinus 

 and of the weight, in the rate of the responsive down-movement, still remains 

 to be determined. A satisfactory way of solving the problem would lie in 

 the study of the characteristics of response-records taken under three 

 different conditions : (1) When the leaf is helped in its fall by its weight ; 

 (2) when the action of the weight is eliminated ; and (3) when the fall has to 

 be executed against an equivalent weight. An approximation to these con- 

 ditions was made in the following manner. We may regard the mechanical 



