( ( ( White and ) gray ) ( matter . ) )
(ROOT (S (NP (NNP White) (CC and) (NNP gray)) (VP (VBP matter)) (. .)))
White and gray matter.
(ROOT (S (NP (NP (JJS Most)) (PP (IN of) (NP (DT the) (JJ gray) (NN matter)))) (VP (VBZ is) (PP (IN on) (NP (NP (DT the) (NN surface)) (PP (IN of) (NP (DT the) (NN brain))))) (, ,) (S (VP (VBG surrounding) (NP (JJ white) (NN matter))))) (. .)))