MODIFICATION OF SUCTIONAL RESPONSE 



375 



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

 per minute. 



(b) Action of moderate rise of temperature. — 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 mm. per minute. On now 



Fig. 159. Curve showing 

 Normal Suction at 23 C, 

 Increased Suction at 35 ° 

 C, and the After-effect 

 persisting on Return to 

 Normal Temperature 



This experiment was carried 

 out on the same specimen 

 as the last. 



Fig. 160. 



Method of Hydrostatic 

 Balance 



A short length of stem, P, has its as- 

 censional water-movement balanced 

 by superincumbent water-column of 

 variable height. 



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 





