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
Naked short selling a price rise. In 2008, the SEC banned what it called "abusive naked short selling" in the United States, as well as some other jurisdictions, as a method of driving down share prices. Failing to deliver shares is legal under certain circumstances, and naked short selling is not "per se" illegal. In the United States, naked short selling is covered by various SEC regulations which prohibit the practice. Critics, including Overstock.com's Patrick M. Byrne, have advocated for stricter regulations against naked short selling. In 2005, "Regulation SHO" was enacted; requiring that broker-dealers have grounds to believe that shares will be