Take two empty cups (cup A and cup B) and fill cup A with water. Take a length of wet cloth and run it from the bottom of cup A to the bottom of cup B, while the cups are standing next to each other on a table. Wait a long time. The cloth will wick water from cup A to cup B until the water levels are equal in the two cups, just like a siphon would. My question is how does the information of the water level in cup A get transmitted through the cloth to the water in cup B?
In the case of a siphon, this information is transmitted as a pressure gradient through the tube that is acting as the siphon. This requires that the tube walls sustain compressive (and sometimes tensile) forces, so that water pressure varies with height throughout the tube length. But in the case of a cloth wick it is capillary forces that pull the water along. The water all along the cloth has free surfaces exposed directly to air, and so presumably at or close to atmospheric pressure. So if there are no semi-rigid external walls to contain the water flowing along the cloth, how doe sit transmit pressure information?