MODIFICATION OF SUCTIONAL RESPONSE 381 



Hydraulic Method of Balance will be found most sensitive : 

 for ordinary purposes, however, the unbalanced Shoshun- 

 graph is simple and efficient ; and in the investigations which 

 follow I shall use this method only. 



Explanation of suction, when the root is killed by 

 boiling water. — I shall now take up the apparently anoma- 

 lous case in which, when the root has been killed, by pouring 

 boiling water over it, the suction of the plant is nevertheless 

 maintained. In such an experiment, the normal record was 

 first taken, and on allowing boiling water to enter the plant- 

 chamber there was a steep rise in the record, showing the 

 excitatory action due to the application of hot water. The 

 boiling water was now passed in continuously for several 

 minutes, so as to ensure the killing of that portion of the 

 plant which was immersed in the vessel. On allowing the 

 water in the vessel to return to the temperature of the room, 

 it was found that suction continued, at an even greater than 

 the original normal rate. 



This result would at first appear to show that protoplas- 

 mic activity had nothing to do with the ascent of sap. And 

 the objection would have been fatal, if the rhythmic activity 

 which produces suction had been confined to the roots alone. 

 But such activity is present to a greater or less extent 

 throughout every zone of the plant, and it is by the com- 

 bined action of all these that the ascensional movement is 

 maintained (p. 376). Thus, when hot water is poured on the 

 root, its first effect is a sudden increase of the activity of that 

 organ, by which warm water is carried to the higher zones, 

 there as a stimulating agency to increase this rhythmic 

 activity. It must be remembered that on reaching the 

 stem above the vessel, the hot water itself is considerably 

 cooled. Hence the only portion of the plant which is killed 

 is that which is actually immersed in the boiling water, 

 or in immediate contiguity with it. The unkilled portions 

 above continue their suctional activity unabated. 



I have said that the suction, on the return of the water 

 to its old temperature, continued to take place at a greater 



