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 10 1 seconds, of which the down 

 movement was accomphshed 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 '9 mm., the 



