Surface tension

Water is a wonderful liquid, with cohesive and adhesive properties. This is one of the reasons for lovely shapes like this!

Water molecules are good at 'sticking' together (the cohesion bit) and they are also rather nifty at sticking to other substances (adhesion). When water evaporates from the little pores on undersurfaces of leaves, it is the stickability that draws more water up the stem from the roots.

Did you know that the girth of a tree during the daytime is narrower than at night? During the day when water evaporates from leaves the negative tension 'sucks' water upwards and causes the tubes transporting it to draw in a bit. Just like if you suck on a paper straw too hard you can collapse it!

There you go - the wonders of transpiration :)

And water. Saturdays are great for wondering about stuff.