(S (S (BASENP (NN Naturism)) (VP (VBZ has) (NP (BASENP (NNS roots)) (VP (VBN traced) (PP (IN from) (NP (BASENP (DT the) (NN start)) (PP (IN of) (BASENP (DT the) (JJ 20th) (NN century))))))))) (PERIOD .))