The Collaborative International Dictionary of English v.0.48:
Mesocarp \Mes"o*carp\, n. [Meso- + Gr. karpo`s fruit.] (Bot.) The middle layer of a pericarp which consists of three distinct or dissimilar layers. --Gray. [1913 Webster]WordNet (r) 3.0 (2006):
mesocarp n 1: the middle layer of a pericarp