This is the xylem tissue that develops just behind a growing tip in a vascular plant. The growing tips of a plant - mostly stem tips and rot tips - are packed full of rapidly dividing cells that go on to form new 'adult' tissue. They go through a process of becoming much bigger and then develop into specialised tissues. One of the first to develop is protoxylem, so that water can be brought directly to the new cells and satisfy their need for plenty of fluid.

the first formed primary xylem, consisting of annular and spiral (helical) vessels.

the first primary xylem to differentiate and mature, usually before and during elongation of the axis; protoxylem cells are generally smaller in diameter than metaxylem