10 



measuring and recording the responses of plants to various 

 stimuli. Following is an abstract of the paper compiled from 

 notes furnished by Professor Bose : 



The effect of stimulus impinging on a responding tissue is to 

 induce a fundamental molecular derangement. This condition 

 of derangement constitutes excitation. On the cessation of 

 stimulus, there is a slow recovery, the tissue returning to its 

 original condition. This molecular reaction is itself beyond our 

 scrutiny, but it may be shown that we can gauge its intensity 

 and extent by the observation and record of certain concomitant 

 changes induced by it in the responding tissue. Amongst these 

 are (i) changes of form, manifested as mechanical response, and 

 (2) changes of electrical condition, which may be recorded as 

 electrical response. 



The intensity of the responsive change will obviously depend 

 on the two factors of strength of stimulus and physiological con- 

 dition of the tissue. Hence, when stimulus is constant, the am- 

 plitude of response gives us a measure of the physiological con- 

 dition. Now we know that the changing environment must 

 induce unknown changes in this physiological condition, of 

 which there is no outward sign. But we are here enabled to 

 make the plant itself reveal its condition, by the reply it makes 

 to the blow of a stimulus. A stimulating agent will exalt, and 

 a depressing agent diminish or abolish, this response. We have 

 thus a means of attacking the deeper problem of the physiolog- 

 ical variation in an organism. 



The speaker had been able to overcome the numerous diffi- 

 culties which occur in connection with the automatic recording of 

 the mechanical response of the plant, by devising three types of 

 instrument. These are (i) the oscillating recorder, (2) the op- 

 tical lever, and (3) the balanced crescograph. 



In the oscillating recorder, the recording lever is made of light 

 aluminum wire and is suspended vertically on jewelled bearings. 

 This lever is L-shaped, and the shorter arm, at right angles to 

 the longer, is attached to the responding leaf The great advan- 

 tage conferred by the oscillating recorder lies in the fact that the 

 friction of the writing point against the recording surface is prac- 



