long section: Cucurbita stem common name: Pumpkin/Squash magnification: 100x

The vascular bundles are bicollateral; the central xylem is bound by an inner and outer cambium, and topped by a larger outer and a smaller inner phloem. Phloem consists of large clear sieve tubes with pitted cell walls and sieve plates, phloem parenchyma and small narrow green stained companion cells. Many sieve plates have deposits of a mucoid p-protein that forms as part of the trauma response in injured phloem. Xylem is well developed with numerous protoxylem evident towards the inside, and very large metaxylem to the outside of the bundles. Xylem consist primarily of large vessels and xylem parenchyma; tracheids and fibers are rare. Walls of xylem vessels have lignin free pits and lignin thickenings that form rings, spirals, networks and solid blocks. The vascular bundles are separated by zones of internal parenchyma.