There are many difficulties inherent in adducing citational evidence unsupported by frequency.
( There ( ( are ( ( many difficulties ) ( inherent ( in ( adducing ( ( citational evidence ) ( unsupported ( by frequency ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (EX There)) (VP (VBP are) (NP (NP (JJ many) (NNS difficulties)) (ADJP (JJ inherent) (PP (IN in) (S (VP (VBG adducing) (S (NP (JJ citational) (NN evidence)) (ADJP (JJ unsupported) (PP (IN by) (NP (NN frequency))))))))))) (. .)))
There are many difficulties citing evidence by frequency. 
( There ( ( are ( ( many difficulties ) ( ( citing evidence ) ( by frequency ) ) ) ) . ) )
(ROOT (S (NP (EX There)) (VP (VBP are) (NP (NP (JJ many) (NNS difficulties)) (VP (VBG citing) (NP (NN evidence)) (PP (IN by) (NP (NN frequency)))))) (. .)))