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 Diversity Seeds of Diversity Seed of Diversity, Semences du patrimoine, is a Canadian charitable organization that aims to "search out, preserve, perpetuate, study, and encourage the cultivation of heirloom and endangered varieties of food crops", particularly Canadian plants, and to educate the public about their use. It has been called "The Canadian NGO leader in two key areas of food system sustainability: crop genetic diversity and the redesign of pollination strategies". Seeds of Diversity originated in 1984 as the Heritage Seed Program of the Canadian Organic Growers organization. Members of Seeds of Diversity propagate and share seeds and other plant material,