The enlarged basal part of a hair within the skin[BTO]. The root of the hair ends in an enlargement, the hair bulb, which is whiter in color and softer in texture than the shaft, and is lodged in a follicular involution of the epidermis called the hair follicle. [Wikipedia]. [ http://purl.obolibrary.org/obo/BTO_0000555 http://en.wikipedia.org/wiki/Hair_root ]