326 RESEARCHES ON IRRITABILITY OF PLANTS 



low temperature. The critical point is somewhat modified 

 by the tonic condition of the specimen. With vigorous 

 specimens the temperature at which arrest takes place 

 may be as low as 17° C. 



Fig. 168. — Effect of rapid cooling by ice water applied at 

 the moment marked by arrow. Note arrest at systole 

 and gradual revival on warming, the pulsations exhibiting 

 staircase increase. 



There are certain interesting points in connection with 

 the arrest brought about by cooling. Two series of records 

 are here given in which the arrest was quickly brought about 



Fig. 169. — Magnified record given by a different specimen of 

 arrest of pulsation by cooling and subsequent revival by 

 warming. Note extension of diastole during warming, 



by the application of cold water to the pulvinule. The 

 leaflet was then allowed to return to the temperature of the 

 room, with the revival of pulsatory activity. The entire 



