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
Seeds of Peace proficiency in English and leadership skills, local politics, general knowledge, and are selected on the basis of interviews and written essays. Many of the first time campers are chosen by the Ministries of Education or other government agencies in their respective countries. John Wallach's vision focused on leaders of the next generation—on Seeds who will one day become change-makers in their communities and generate political, social and economic impact. Delegation Leaders are educators from the countries in conflict; they take part in the selection and orientation of Seeds at home. They accompany the Seeds to and from camp. At the