Syringa reticulata subsp. pekinensis capsules. The bark is a red-brown color. They grow well in moist, well-drained soil. They prefer full sun but will tolerate light shade. Syringa reticulata subsp. pekinensis Syringa reticulata subsp. pekinensis (formerly known as "Syringa pekinensis"), also known as the Pekin lilac or the Chinese tree lilac, grows in an open, multi-stemmed form to a height of , with a spread of . They are native to northern China but grow in USDA hardiness zones 3 through 7. It is grown as an ornamental tree in Europe and North America. Pekin lilacs have arching branches and ovate dark green leaves
What Is and What Should Never Be descending riff [of "What Is and What Should Never Be"] is amazing: It's like a bow is being drawn back, and then it releases. The rhythm of the vocals is almost like a rap. It's insane — one of their most psychedelic songs." This was also one of the first songs recorded by the band for which Robert Plant received writing credit. According to rock journalist Stephen Davis, the author of the Led Zeppelin biography "Hammer of the Gods: The Led Zeppelin Saga", the lyrics for this song reflect a romance Plant had with his wife's younger sister. "What Is