6 RESEARCHES ON IRRITABILITY OF PLANTS 



concomitant curve. For this there must be an axis, sup- 

 ported on frictionless jewelled bearings, and carrying two 

 arms of a horizontal lever and a thin vertical wire with a 

 bent tip, to serve as the writer. The different parts, as far 

 as possible, should be made of aluminium, to secure the 

 utmost lightness. A point of the petiole of the responding 

 leaf would be attached by a silk thread to one arm of the 

 lever, the other having on it a small weight, to act as counter- 

 poise. On the fall of the leaf, under ex- 

 citation, it would pull down with it the 

 attached arm of the lever. The vertical 

 writer would then also move, say, to 

 the left. If the finely pointed bent end 

 of the writer were to press lightly 

 against the smoked surface of a glass 

 plate, which was allowed to fall, at a 

 uniform rate, by means of clockwork, 

 a curve would then be traced which 

 would not only record the responsive 

 movement and recovery but also give 

 their time-relations (fig. i). To obtain 

 the latter, it would be necessary to 

 know the rate of movement of the 

 plate on which successive vertical lines 

 might be traced by a time-marker at 

 intervals of, say, one minute. 



In order to find out the absolute 

 movement of the leaf we must know 

 the degree of magnification or reduction that has been 

 effected by the recording arrangement. This will depend upon 

 the relative lengths of the writer and the lever, and the 

 distance of the point of attachment on the leaf from the 

 pulvinus. When the lengths of the lever-arm and the 

 writer are equal, then the writer will describe a movement 

 which is equal to that of the point of leaf -attachment. By 

 shortening the arm of the lever to half the length of the 

 writer, we should obtain the magnification of two. This 



Fig. i. — Diagrammatic 

 representation of Re- 

 sponse Recorder. 



