Transpiration stream

The continuous upward flow is the transpiration stream. Evaporation at the leaf helps pull the column of water upwards from the roots; the roots do not simply push it to the top. Mineral ions travel with the water.

Because the xylem contains a continuous column of water, this produces a flow from the roots, up the stem and into the leaves. That flow is the transpiration stream.

As water leaves, more water is pulled up the xylem in the transpiration stream and absorbed from the soil to replace it. Consequently, an environmental factor that increases transpiration will usually increase the plant’s rate of water uptake as well. The two processes are closely connected but are not identical: transpiration is water loss from the shoot, whereas uptake is water entering the plant, mainly through its roots.

The continuous movement from roots towards leaves is called the transpiration stream.