Real Dictionary

protostele in American English
a simple, primitive arrangement of conducting tissues in stems and roots of certain lower plants, consisting of a solid cylinder of xylem surrounded by a layer of phloem
noun: the solid stele of most roots, having a central core of xylem enclosed by phloem

protostele in British English
noun: a simple type of stele with a central core of xylem surrounded by a cylinder of phloem: occurs in most roots and the stems of ferns, etc