The ancestors of the word osmosis mean a pushing impulse and osmosis is the scientific term for a law of nature which deals with the behavoir of liquids. The operation of osmosis is vital to the living tissues of both plants and animals and most of the time we do not notice it.

All liquids must obey the law of osmosis. Water, of course, tends to flow downhill   but under certain conditions it can be made to flow uphill. Our plumbing systems force water to flow uphill under pressure. Plants need to make water flow up from their roots to their leaves and, instead of using metal plumbing, they let osmosis do the job for them.

Pure water with no dissolved chemicals is very rare. Most liquids are solutions with more or less amounts of dissolved chemicals   and in osmosis, this more or less makes all the difference. Osmosis works when a weaker and a stronger solution are separated by a layer of membrane tissue. The weaker solution, with fewer dissolved chemicals, seeps through the membrane to join the stronger solution. It may pass up, down or sideways, but the weak will always join the strong.

Membrane is skin tissue and thin, tough membrane layers enfold the heart and other vital internal organs. Layers of membrane also enclose the living cells of plants and animals. And the law of osmosis operates wherever there are liquids separated by membrane tissues. In our bodies, weak solutions are forever seeping through to join stronger solutions as osmosis works to circulate and regulate the balance of vital liquids.

In the plant world, the stronger solutions are the sugar rich saps which fill the cells of the leaves and growing wood. The weaker solutions are the watery mixtures of dissolved chemicals in the ground. Here, the weak and strong are separated by the filmy membranes which enclose the roots and the fine hairs which sprout from them. Water, with traces of dissolved chemicals vital to the growth of the plant, seeps through the cell wall and joins the richer chemical inside. This simple operation of osmosis is one of the methods a plant uses to get water from the ground up to its leaves.

Osmosis works on a small scale, from cell to cell. But billions of these small operations working together exert tremendous pressure. This pressure of osmosis helps a plant to keep its leaves and  stems firm. It is also the pressure a plant uses to push its growing roots through a concrete pavement,