RHYTHMIC RESPONSE IN PLANT AND ANIMAL 349 



Fig. 146. Curve showing Relation between 

 Temperature and Period of Pulsation in 

 Desmodiiivi 



Abscissa represents temperature, and ordinate 

 time, in tenths of a minute. 



experiment was carried out by mounting a detached petiole 

 containing the motile leaflets at one end of a limb of a 

 U-tube. Any desired 

 pressure could be ex- 

 erted by varying the 

 height of the second 

 limb, which was con- 

 nected with the first by 

 india-rubber tubing. By 

 exerting internal pres- 

 sure in this manner, 

 I was able to pro- 

 duce vigorous rhythmic 

 movements of leaflets 

 which were, before this, 

 in an absolutely qui- 

 escent condition. The 

 beneficial effect of this constant internal pressure was further 

 seen demonstrated by the extreme regularity and persistency 

 of the rhythmic beats. 

 Even in the best season 

 of the year, the pulsations 

 are irregular, and come to 

 an occasional stop ; but 

 under the action of internal 

 pressure, I have found the 

 detached leaflet to main- 

 tain its rhythmic activity 

 unimpaired for nearly one 

 hundred hours. In con- 

 nection with this question 

 of the increase of inter- 

 nal pressure, it should be 

 mentioned here that, after 

 the normal condition of 

 turgidity has been established, a further increase of internal 

 pressure is found to increase the frequency of pulsation. 



Fig. 147. Curve showing Relation 

 between Temperature and Period of 

 Pulsation in the Heart of a Frog 



Ordinate represents time, in tenths of a 

 second. 



