296 RESEARCHES ON IRRITABILITY OF PLANTS 



these movements in their various phases. The movements 

 themselves are relatively slow, much slower than the con- 

 tractile movement of Mimosa. In that case we saw that 

 the movement of the fall was accomplished in about 2 seconds 

 but with Desmodium the down movement may occupy as 

 long as 40 seconds. I was able to determine the different 

 rates of movement in Desmodium by making the recording 



Fig. 143. — Record of a single pulsation of Desmodium; magnification 

 25 times. Successive dots at intervals of a second. 



plate oscillate to and fro once in a second or once in two 

 seconds. 



In fig. 143 is given a record of a single pulsation, mag- 

 nified 2 - 5 times and taken on a fast-moving plate, the 

 successive dots being at intervals of a second. The period 

 of an entire pulsation was 101 seconds, of which the down 

 movement was accomplished in 41 seconds and the up 

 movement in 60 seconds. The spacing of the successive 

 dots at once gives a visual representation of the changing 

 rate. It is noticed that the leaflet attains its maximum 

 rate during the fourteenth second of its downward journey. 

 The maximum rate of the down-movement is - o, mm., the 



