Colour your own flowers

Explanation

Land plants have a problem, the water, minerals and other nutrients they need are in the ground but they are needed in their leaves which need to have access to the sun, so they have to be up in the air. This means the plants need a mechanism for transporting water with dissolved nutrients up their stems to the leaves.

They do this using a tissue called xylem, which is made of thousands of tiny tubes, which run from the roots each to a different part of the plant.

Normally the roots sort out what the plant wants and allows that into the xylem. Bit if you cut the stem, you loose the filtering of the roots and the xlem will suck up whatever they are sitting in. This means that you can keep a cut flower hydrated and fairly healthy for a couple of weeks if you put the right nutrients into the water.

It also means that if you put something coloured into the water it will be sucked up all the way into the leaves and the petals.

How does the Xylem work?

The xylem is made up of incredibly thin tubes full of water. Each tube runs from the roots to somewhere in a leaf petal or fruit. If water evaporates from the leaf that will concentrate the sugars and salts in the cells there. By the process of osmosis water is moved from the xylem into the cells. Osmosis is  the same reason that putting salt on a snail will dry the snail out.

Removing water from the top of the tube reduces the pressure there, this causes water to flow up the tube all the way from the roots.

 How does the tube stay full of water?

 The tubes are made of a material which is attracted by and attractive to water (hydrophyllic) this means that energy is released by the water wetting the material. Lots of other materials are hydrophyllic, including paper glass and your fingers.

If you put a hydrophyllic object through the surface of a body of water it will attract the water a lift the level of the water around the object. This raised area is called a meniscus.

If you put two hydrophobic objects close together they are both attracting the small amount of water between them, so there is more attraction to lift less water, so the meniscus can rise  higher than normal.

If you get the two objects very close together they will lift the water even further.

If you put an object which is attracted to water in a bowl of water, the surface rises up either side to form a meniscus	If you move two objects close together then the mensicus in the middle rises up.	If they are very close together then the meniscus rises a long way, as there is less weight of water to lift.

The tubes in xylem are immensely small, down to 0.01mm across, so the water can rise up between them a huge distance.