A carrot is a taproot. Unlike more fibrous roots, which develop later in the plant's life cycle, the taproot is the first root to emerge from the germinating seed, called the radicle. For most plants, the radicle dies and is replaced with a branching, spreading system of roots.
Carrots can vary in shape and size, but most carrots are conical in shape. The taproot itself is composed of outer phloem cells and inner xylem cells. The phloem, also known as the cortex, is where sugars are transported from the leaves down into the roots. The xylem, or core, transports water and minerals from the soil up to the leaves. Most carrots have been selected to have more cortex than core, hence the sweet taste.