36 RESEARCHES ON IRRITABILITY OF PLANTS 



point, we shall call the Apex Time. The pulvinus remains 

 for a short time in its contracted condition. 



Third and lastly, recovery of the pulvinus from the 

 effect of stimulus begins to take place, with consequent 

 re-erection of the leaf. This process of recovery is 

 very much slower than the responsive fall. While the 

 responsive fall is a matter of a few seconds only, the 

 re-erection or recovery requires several minutes. This 

 recovery, again, is at first rapid and at the end rela- 

 tively slow. 



Quantitative measurements of these different phases 

 may, as we shall see, be derived from the response-curve 

 itself. In obtaining these, there are two elements to be 

 measured — ^namely, the extent and the rate of movement. 

 The amplitude or height of the curve gives a measure of 

 the amount of movement. Magnification or reduction of 

 the record results, as we have seen, from two elements of 

 adjustment — namely, the ratio between the horizontal 

 arm of the lever and the length of the recorder, and the 

 ratio between the distance of thread-attachment from the 

 pulvinus and the entire length of the leaf. 



In the record given in fig. 12 the length of the vibrating 

 recorder was 10 cm. and the thread-attachment with the 

 leaf was made with the horizontal arm of the lever at a 

 distance of 5 cm. from the fulcrum rod. The magnification 

 of the writing-lever was therefore 2. The total length of 

 the responding leaf was g cm. But the thread-attachment 

 to the horizontal lever was made at a point on the petiole 

 3 cm. from the pulvinus. The responsive movement of 

 that particular point on the petiole was therefore reduced 

 to one-third the movement of the tip of the leaf. Thus 

 we have a reduction to one-third brought about by the 

 selection of the point of attachment on the petiole, and a 

 magnification of two, due to the writing-lever. The record 

 obtained represents in this case the actual movement of the 

 tip of the leaf, reduced to two-thirds. 



As regards the time-measurements of the responsive 



