MODIFICATION OF SUCTIONAL RESPONSE 



375 



degree, being now about seven instead of eight cubic mm. 

 per minute. 



{b) Action of moderate rise of teviperatiire. — I next tried 

 the effect of a rise of temperature. This experiment was per- 

 formed with the same specimen as the last, in which the 

 return normal rate of suction at 23° C. had already been 

 determined to be seven cubic ram. per minute. On now 



I ir.. 159. Curve sliovving 

 Normal Suction at 23° C. , , 

 Increased Suction at 35° 

 C, and the After-effect 

 persisting on Return to 

 Normal Temperature 



Tliis experiment was carried 

 out on the same specimen 

 as the last. 



A short length of stem, i', has its as- 

 censional water-movement ])alanced 

 hy superincumbent water-column of 

 variable heitrht. 



applying water at 35° C. it will be seen that a very steep rise 

 was induced in the curve, indicating an increased suctional 

 rate of fifty-eight cubic mm. per minute, more than eight 

 times the rate at 23° C. On now once more substituting 

 water at 23° C. the rate became lowered, though not to the 

 original degree (fig. 159). It must be remembered, with 

 regard to this, that the movement of sap depends on the cell- 

 activity of the entire plant, and that the tissue has by this 



