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 (Agents of S.H.I.E.L.D.) Seeds (Agents of S.H.I.E.L.D.) "Seeds" is the twelfth episode of the first season of the American television series "Agents of S.H.I.E.L.D.", based on the Marvel Comics organization S.H.I.E.L.D. (Strategic Homeland Intervention, Enforcement and Logistics Division), revolving around the character of Phil Coulson and his team of S.H.I.E.L.D. agents as they investigate attempted murder at the S.H.I.E.L.D. Science Academy. It is set in the Marvel Cinematic Universe (MCU), sharing continuity with the films of the franchise. The episode was written by Monica Owusu-Breen and Jed Whedon, and directed by Kenneth Fink. Clark Gregg reprises his role as Coulson from the film