Opuntia macrocentra populations of "Opuntia macrocentra" are found in Arizona, New Mexico, Southwestern Texas, and Northwestern Mexico. This cacti is a slow growing perennial that inhabits a wide range of soil substrates and habitat types. It can be found below the elevation of 5000 ft in areas of sandy desert flats, rocky hills, or valley grasslands. "Opuntia macrocentra" is an upright spreading shrub, usually growing from tall. Individuals occasionally reach in height. The stem is blue-gray, blue-green, or purplish in color. The purple pad color is the most intense at the edges of the pad or around the areoles. The purple color
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