The obvious purpose of the roots of plants is to serve as an anchorage or holdfast. Their other and equally important function is to secure food for the plant, a process that will be described in the part devoted to Plant Behavior. Certain plants bear no roots and attach themselves to the roots of other plants in which case they literally steal their food, as does the mistletoe and some others.
Roots are of various kinds, depending upon the soil in which they grow and upon the kind of plant to which they are attached. In the case of annuals, which live only one year, as does the purslane, and biennials, which live only two years, as does the fringed gentian, the roots are mostly fibrous ([Figure 1]) and apt to be only slightly under the surface. In perennials, which live many years, such as the dandelion, the root is deeper and forms what is known as a taproot ([Figure 2]). In shrubs and trees they are harder, woodier, and often penetrate to great depths.
If we examine the roots of a tree, we find a large part of them are woody, often as thick as the smaller branches, and it is only toward their extremities that they branch out into the multitude of rootlets