The Probert Encyclopaedia of Nature

TAP ROOT

Tap root is the name given to the primary root of most dicotyledonous plants. It is the continuation of the stem below the cotyledons, and from it the secondary or lateral roots arise. In many plants the tap root acts as a storehouse of food, becoming thickened and round, as in the turnip, or conical as in the carrot.
Research Tap Root