Some species such as the fly agaric and psilocybin mushrooms are used for the psychoactive drugs that they contain.[26] These are the focus of academic study and intense debate in the field of ethnomycology. In the 1950s, the American banker Robert Gordon Wasson participated in a Mazatec psilocybin mushroom ritual, and wrote an influential but controversial book claiming that the Soma mentioned in the Rigveda was Amanita muscaria, the fly agaric.[lower-alpha 1][28][29][27] The mycologist John Ramsbottom however confirmed one element that Allegro later wove into his theory, stating in 1953 that the tree of the knowledge of good and evil fresco[lower-alpha 2] in the Plaincourault Chapel depicted Amanita muscaria.[lower-alpha 3][30]