phloem (n.)

in botany, "cells and fibers forming the softer, bast portion of a vascular bundle," 1870, from German phloëm (1858), coined by German botanist Karl Wilhelm von Nägeli from Greek phloos, phloios "bark of trees, rind, skin of a fruit," a word of uncertain origin (perhaps from an extended form of PIE root *bhel- (2) "to blow, swell"), + passive suffix -ema.