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 Change (book) Made Men Rich" covering timber, wine, rubber, and tobacco. David E. Allen writing in "Medical History" described it as "a thoughtful, thought-provoking, extremely readable work" It has been recommended reading and studied at universities and has been reviewed by the "Library Journal", "The American Historical Review", and "The Atlantic". Seeds of Change (book) Seeds of Change: Five Plants That Transformed Mankind is a 1985 book by Henry Hobhouse which explains how the history of the world since Columbus linked America to Europe and has been changed by five plants. It describes how mankind's discovery, usage and trade of sugar, tea,