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
Naked yoga and other ascetic groups in the dharmic religions. A notable example is the order of sadhus known as the Nagas who use nudity as a part of their spiritual practice of renunciation. The word "Nāga" comes from NAG (snake) which signifies power in Hindu philosophy. The word sadhu derives from sadhana meaning spiritual practice. Members of the sect considered nudity a way of rejecting the material side of life. Celibacy and disregard of the harsh outside conditions were among the key ideas of their philosophy. They practiced naked yoga to tame their desires, identify with their physical bodies and to