A Self-Recording Porometer and Potometer. 361 
Owing to contraction of the stretched rubber connection 
between F and C, the lower end E' of the tube EE' is pressed into 
the hole in the rubber cork and the tube CC consequently closed 
at its lower end. The water taken from the reservoir K to replace 
that lost by transpiration from the branch is compelled therefore to 
flow along the track EE’ ABB' A' GH. 
The mercury index, starting at the lowest point B of the tube 
ABB'A', is drawn along the narrow part of this tube in the 
direction BB‘. As it makes contact with the terminals tt (which 
are connected with the recorder) a circuit is established and 
the recording pen engages with the drum as described for the 
