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
Unwins Seeds A1(M) just north of the A14 Alconbury junction. It has garden seeds for flowers and plants. It has the largest share of the UK amateur seed market. Unwins Seeds Unwins Seeds is a British seed company based in Alconbury Weston, Huntingdon in Cambridgeshire. "The Times" describes Unwins as "a firm that has grown ... to become one of the most familiar features of Britain’s horticultural landscape", and the BBC calls the company "world-famous". Unwins Seeds was formed in 1903 by William Unwin by selling sweet pea seeds. His son Charles, who had an interest in sweet peas, joined the business