( ( ( Protons and ) neutrons ) ( ( are ( composed ( of ( ( ( ( three quarks ) apiece ) , ) ( ( bound together ) ( by gluons ) ) ) ) ) ) . ) )
(ROOT (S (NP (NNS Protons) (CC and) (NNS neutrons)) (VP (VBP are) (VP (VBN composed) (PP (IN of) (NP (NP (NP (CD three) (NNS quarks)) (NP (RB apiece))) (, ,) (VP (VBN bound) (ADVP (RB together)) (PP (IN by) (NP (NNS gluons)))))))) (. .)))
Protons and neutrons are composed of three quarks apiece, bound together by gluons.
(ROOT (S (NP (EX There)) (VP (VBP are) (NP (NP (CD three) (NNS quarks)) (PP (IN in) (NP (DT each) (NN proton) (CC and) (NN neutron))))) (. .)))