The peyote and mescaline relations stated above are incorrect.  There are multiple kinds of pyschedelic cacti, peyote being the king daddy.  Mescaline is the most active ingredient in these cacti.  But, peyote contains multiple others psychedelics, tryptamines, etheogens, that make it what it is.  Sure, mescaline is the most active pyschoactive in peyote, but the others make the trip an entirely different one.