( ( In ( the ( brain ( white matter ) ) ) ) ( ( ( is ( surrounded ( by ( grey matter ) ) ) ) ( most ( of ( the time ) ) ) ) . ) )
(ROOT (S (PP (IN In) (NP (DT the) (NN brain) (JJ white) (NN matter))) (VP (VBZ is) (VP (VBN surrounded) (PP (IN by) (NP (JJ grey) (NN matter))))) (NP (NP (JJS most)) (PP (IN of) (NP (DT the) (NN time)))) (. .)))
In the brain white matter is surrounded by grey matter most of the time.
(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))))) (. .)))