metaxylem

詳細解釋：

met.a.xy.lem

n.Botany （名詞）【植物學】
The part of the primary xylem that differentiates after the protoxylem and is characterized by broader vessels and tracheids.
後生木質部：初生木質部中不同於原生木質部的一部分，以更寬的導管和管胞為特徵