298 RESEARCHES ON IRRITABILITY OF PLANTS 



specimen taken on a slower-moving plate (fig. 145). This 

 record shows the extreme uniformity of these pulsations. 

 How uniform the time-relations are will appear from the 

 tabular statement below, where the intervals of time are 



Fig. 145. — Series of automatic pulsations of Desmodium. 

 Successive dots at intervals of 2 seconds. 



measured between the attainment of highest and lowest 

 positions : — 



Table showing Periods of Down and Up Movement in 

 Desmodium Pulsation 



These figures are typical of the movement of Desmodium 

 leaflet under normal conditions in the summer season. In 

 winter the rate is very much slower, the period of an entire 

 pulse being then as long as 4 minutes. 



Various other factors modify either the amplitude or 

 frequency of the pulsatory movement. One factor which 

 induces a pronounced change is that of temperature. The 



