Fern fronds are the leaves of ferns. They are a major organ of a fern and range significantly between species. Some species of tree ferns have fronds that grow as large as 5 m long while other species are limited to growing frond only 1 cm in length.
Cerium is a soft, ductile, silvery-white metallic chemical element with symbol Ce and atomic number 58. Cerium tarnishes when exposed to air, and it is soft enough to be cut with a knife. Cerium is the second element in the lanthanide series, and while it often shows the +3 state characteristic of the series, it also exceptionally has a stable +4 state that does not oxidise water.
1 The modern element symbol for mercury is Hg, which is the symbol for another name for mercury: hydrargyrum. 2  Hydrargyrum comes from Greek words for water-silver (hydr-means water, argyros means silver). 3  Mercury is a very rare element in the Earth's crust. 4  It accounts for only about only 0.08 parts per million (ppm). Mercury is a very rare element in the Earth's crust. 2  It accounts for only about only 0.08 parts per million (ppm). 3  Mercury generally is not allowed on aircraft because it combines so readily with aluminum, a metal that is common on aircraft.