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 naked short selling. In 2008, SEC chairman Christopher Cox said that the SEC "has zero tolerance for abusive naked short-selling" while implementing new regulations to prohibit the practice, culminating in the September 2008 action following the failures of Bear Stearns and Lehman Brothers amidst speculation that naked short selling had played a contributory role. Cox said that "the rule would be designed to ensure transparency in short-selling in general, beyond the practice of naked short-selling." As with the prevalence of naked shorting, the effects are contested. The SEC has stated that the practice can be beneficial in enhancing liquidity in