Helianthus old root, primary xylem core

This image to the right shows the central core of a mature Helianthus root. The primary xylem forms a four-pointed 'star' and you can see that the protoxylem (unlabelled arrows point to the protoxylem) is exarch, and that the metaxylem (MX) is endarch. Some , non-lignified parenchymatous cells  surround the core, which is surrounded by large-diameter secondary xylem vessels.