358 RESEARCHES OX IRRITABILITY OF PLANTS 



diastole is found to take place in the pulsation of Desmo- 

 dium by the application of ligature below the motile organ 



IP- 303)- 



The pulsating leaflet of Desmodium, like the pulsating 

 heart, is more susceptible to excitation at diastole than at 

 systole. An extra pulsation is induced by an induction 

 shock applied during the diastolic phase (p. 319). Trans- 

 mitted excitation affects the normal pulsations of rhythmic 

 tissues — animal and vegetal— in a similar manner. In 

 certain circumstances the effect is one of inhibition ; in 

 other circumstances the effect is one of acceleration (p. 320). 



Still more remarkable are the similarities of effect of 

 temperature and of chemical reagents on the rhythmic 

 pulsations in animal and plant. 



Effect of Temperature 



The effect of lowering of temperature on the rhythmic 

 pulsation of Desmodium gyrans is similar to that on the 

 pulsation of a frog's heart. Lowering of temperature 

 enhances the amplitude, but reduces the frequency of 

 pulsation of both. The pulsation of Desmodium leaflet is 

 arrested at the minimum temperature of about 17 C. 

 Arrest takes place at systole ; gradual warming revives 

 the pulsation, which undergoes a staircase increase with 

 enhancing diastolic expansion (p. 326). 



Rise of temperature induces enhanced frequency and 

 diminished amplitude of pulsation. During rise of tempera- 

 ture to about 43 C. there is a tendency of arrest towards 

 diastole. The systolic contraction undergoes continuous 

 diminution during rise of temperature. During the fall of 

 temperature there is a gradual enhancement of systolic 

 contraction (p. 330). The temperature maximum at which 

 arrest of pulsation takes place may be as high as 45 C. 

 Above this temperature there is a tendency to contraction 

 and permanent arrest under heat-rigor. 





