Evolutionary history of plants phloem on the outside. Since xylem cells comprise dead, lignified tissue, subsequent rings of xylem are added to those already present, forming wood. The first plants to develop secondary growth and a woody habit, were apparently the ferns, and as early as the Middle Devonian one species, "Wattieza", had already reached heights of 8 m and a tree-like habit. Other clades did not take long to develop a tree-like stature. The Late Devonian "Archaeopteris", a precursor to gymnosperms which evolved from the trimerophytes, reached 30 m in height. The progymnosperms were the first plants to develop true wood, grown from
Stele of the Vultures vultures after which the stele is named, with the severed heads of the enemies of Lagash in their beaks. The second register shows soldiers marching with shouldered spears behind the king, who is riding a chariot and holding a spear. In the third register, a small part of a possibly seated figure can be seen. In front of him, a cow is tethered to a pole while a naked priest standing on a pile of dead animal bodies performs a libation ritual on two plants spouting from vases. Left of these scenes is a pile of naked bodies surrounded by