Plant roots typically grow downwards towards earth’s gravity. This downwards oriented growth is termed positive gravitropism. When growing through soil, roots can encounter hard clumps of soil, rocks, and other obstacles they must make their way around to penetrate the soil. Root use the process of circumnutation to search the soil for unobstructed paths to follow. At the very tip of roots is covered by a "root ca", which is a group of cells that protects the root apical meristem from making direct contact with objects in the soil that might otherwise damage the meristem cells. Also, the outer cells of the root cap produce a mucilage that helps the root tips slide through spaces in the soil. When a root has depleted the nutrients around it, it grows longer to reach soil were the may be more nutrients. The movie shows 12 days of root growth in an "ant farm-like" chamber.