protoxylem Develops while the vascular tissue (PO:0009015) is still elongating. When protoxylem tracheary elements (PO:0025575) are destroyed they may become obliterated by surrounding parenchyma cells (PO:0000074). Protoxylem has smaller elements than the metaxylem (PO:0000372). PO:0000272 PO_GIT:434 portion of protoxylem tissue (exact) 原生木（質）部 (Japanese, exact) protoxilema (Spanish, exact) plant_anatomy A portion of primary xylem (PO:0000272) tissue that has as part one or more protoxylem tracheary elements (PO:0025575) embedded in parenchyma (PO:0005421) tissue. primary xylem