Which of the following techniques was used by Mitler for collecting phloem sap?

$A$ potometer works on the principle of:

Match the theories given in column-$I$ with the names of scientists listed in column-$II$. Choose the answer which gives the correct combination of the alphabets.

Column-$I$ (Names of theories)	Column-$II$ (Names of scientists)
$(A)$ Relay pump theory	$(p)$ Stocking
$(B)$ Transpiration cohesion theory	$(q)$ Sir $J$.$C$. Bose
$(C)$ Mass flow	$(r)$ Godlewski
$(D)$ Pulsation theory	$(s)$ Dixon and Joly
	$(t)$ Ernst Munch

Stomatal opening and closing is due to the permeability of the guard cell. This fact was revealed by

The principle of working of all potometers is

Comment on the experimental setup shown in the image.
What does this setup demonstrate?