_Parchment._ With regard to the preparation of parchment and other kinds of skin for writing on (_Pergamena_ and _Membrana_) there is little to be said. The skins of many different animals have been used for this purpose both in classical and mediaeval times, especially skins of calves, sheep, goats and pigs. Unlike manuscripts on papyrus, parchment or vellum[16] manuscripts were usually covered with writing on both sides, since the ink does not show through from one side to the other, as it is liable to do on the more absorbent and spongy papyrus paper. For this reason complete or partial erasures were much easier to execute on vellum than on papyrus. The writing was first sponged so as to remove the surface ink, and the traces that still remained were got rid of by rubbing the surface of the vellum with pumice stone. In some cases the manuscript was erased from the whole of a vellum codex or roll, and the cleaned surface then used to receive fresh writing. _Palimpsests._ _Palimpsests_; manuscripts of this class, on twice-used vellum, were called _palimpsests_ ([Greek: palimpsêstos]); see Cic. _Fam._ vii. 18. Several important texts, such as the legal work of Gaius, have been recovered by laboriously deciphering the not wholly obliterated writing on these palimpsests. During the early mediaeval period, when classical learning was little valued, many a dull treatise of the schoolmen or other theological work of small interest was written over the obliterated text of some much earlier and more valuable classical author. _Papyrus MSS._ In some cases it appears that papyrus manuscripts were made into palimpsests, but probably not very often, as it would be difficult to erase the ink on a roll of papyrus without seriously injuring the surface of the paper. Moreover as papyrus manuscripts were only written on one side of the paper, the back was free to receive new writing without any necessity to rub out the original text. The recently discovered treatise by Aristotle on the _Political Constitution of Athens_ has some monetary accounts written on the back of the papyrus by some unphilosophical man of business not many years later than the date of the original treatise. _Papyrus paper._ _Papyrus paper._ The ancient methods employed in the preparation of papyrus paper (_charta_) can be clearly made out by the evidence of existing examples aided by the minute but not wholly accurate description given by Pliny, _Hist. Nat._ XIII. 71 to 83. _Papyrus plant._ The papyrus plant, the _Cyperus Papyrus_ of Linnaeus, (Greek [Greek: byblos]) is a very tall, handsome variety of reed which grows in marshes and shallows along the sides of streams of water. The plant has at the top a very graceful tufted bunch of foliage; its stem averages from three to four inches in diameter, and the total height of the plant is from ten to twelve feet.