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
Sub-provincial division People's Congress in 1985. The conferences: Sub-provincial division A sub-provincial division () (or deputy-provincial divisions) in the People's Republic of China is like a prefecture-level city that is governed by a province, but is administered independently in regard to economy and law. Sub-provincial divisions, similar to prefectural-level divisions, an administrative unit comprising, typically, a main central urban area, and its much larger surrounding rural area containing many smaller cities, towns and villages. The mayor or chairman of a sub-provincial division is equal in status to a vice-governor of a province. Its status is below that of municipalities, which are independent