176 



Professor Jagadis Ch under Bose 



[May L>1), 



response. For obtaining a record, the leaf of Mimosa is attached to 

 one arm of a lever, V ; the other is loaded with a small weight, which 

 acts as a counterpoise. A long wire, W, bent at the tip, is placed at 

 right angles to the lever, and serves as a writer. The tip of this 

 wTiter touches a smoked-glass plate, which is allowed bj means of a 

 clock-work to fall at a definite rate (Fig. 1). An instantaneous 

 electric shock is applied on the leaf -stalk at A. The excitation will, 

 after a time, be propagated from A to the responding pnlvinus at B. 

 inducing the responsive fall of the leaf. After a definite period the 

 leaf recovers from excitations and is re-erected. A complete curve 

 of response is thus obtained in which the ordinate a b represents the 

 intensity of excitation, and the abscissa ac tlie period of complete 



Fig. 2. — Response-Curve of Primary Leaf op Mimosa. 

 The vertical lines below the record indicate intervals of one minute each. 



recovery (Fig. 2). Any condition which increases excitability will 

 also enhance the amplitude of response. Depression, on the other 

 hand, is attended by a diminution of response. At death the response 

 is altogether aboUshed. Thus, by means of testing blows, we are 

 able to make the plant itself reveal those invisible internal changes 

 which would otherwise have entirely escaped us. 



The above is a description of the theoretical method of obtaining 

 response of the plant. In practice numerous difficulties have to be 

 overcome. In the case of muscle-contraction, the pull exerted is 

 considerable and the friction offered by the recording surface con- 

 stitutes no essential difficulty. In the case of plants, however, the 



