The main root of a plant typically grows downwards towards earths gravity. This downwards oriented growth
is termed positive gravitropism. As a root elongates, the cells behind the root apical meristem differentiate, with
some epidermal cells forming root hairs. Root hairs are thought
to function in uptake of water and minerals from the soil.
Arabidopsis root tip growth
This movie shows a close-up view of root and root hair growth in light-grown Arabidopsis seedlings. The roots are growing along the surface of vertically oriented nutrient agar. For this movie, the magnification was about 55X (the movie shows an area 2.0 mm wide by 1.5 mm high). Frames were captured every 20 min and are played back at 8 frames per sec. Note that as some of the root hairs come into contact with the wet agar surface, they appear to darken and thicken.