EXCITATORY CHARACTER OF SUCTIONAL RESPONSE 



The question of the excitatory nature of the ascent of 

 sap may again be tested by the application of anaesthetic 

 agents, such as solution of ether. The record is first taken 

 of the actual rate of suction, and then by quick manipulation 

 of the double key, the water in the plant-vessel down to the 

 base of the specimen is replaced by ether solution. The 

 original rate of suction had in a particular case been 40 

 cubic mm. per minute. After 

 the application, however, this 

 became depressed, and in the 

 course of four minutes under- 

 went a preliminary arrest. 

 This short arrest was suc- 

 ceeded by reversal, or expul- 

 sion, which lasted for fourteen 

 minutes, and then gave place 

 to what was practically per- 

 manent arrest (fig. 220). 



I have occasionally ob- 

 served an interesting variation 

 in the arrest of suction induced 

 by ether. Shortly after the 

 application just described an 

 arrest of suction is induced. 

 This, however, is only pre- 

 liminary, suction after an 

 interval being renewed at a 

 very slow rate. When this 

 has proceeded for some time, 

 the process undergoes a 

 gradual and final arrest. 



It has already been said that though the excitatory 

 reaction is to be regarded as the fundamental cause of the 

 transport of water in the plant, yet there are other factors 

 which undoubtedly contribute to that result. One of these 

 may be the favourable disposition of osmotic substances- 

 for example, the concentration of cell-sap consequent ori 



FIG. 220. Action of Anaesthetics in 

 Abolition of Suction 



Solution of ether substituted for water 

 at point marked with dots . . . Suc- 

 tion abolished within fifteen minutes. 



