I have been growing wheat grass in a container underneath a light inside. I noticed drops of water clinging to the tips of the growing blades and brushed them off thinking they were left from being watered. A few hours later there were more drops.
Thomas Thundat determined it was due to cohesion between water and it's surface, also known as capillary action. This happens when the sides of the container (the tube) are close together, and the water is sucked to the wall, and thus sucked in all directions, but if the walls are "closing in" above, the cohesion is stronger, and it "pulls" the water up. If you look closely, wheatgrass is shaped like a tapering straw, with an inner cylindrical chamber.
Notably Einstein's first white paper was on capilarity.