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
Scope of practice assistant, nurses, dietitians, respiratory therapists, physical therapists, occupational therapists and dentists among many others. Governing, licensing, and law enforcement bodies are often at the sub-national (e.g. state or province) level, but federal guidelines / regulations also often exist. For example, in the United States, the National Highway Traffic Safety Administration in the Department of Transportation has a national scope of practice for emergency medical services. Scope of practice The scope of practice describes the procedures, actions, and processes that a healthcare practitioner is permitted to undertake in keeping with the terms of their professional license. The scope of practice is