( ( ( ( ( ( Pre-chill ( a mortar ) ) and ) ( pestle ( with ( liquid nitrogen ) ) ) ) and ) ( ( grind ( the ( plant tissue ) ) ) ( to ( ( a ( fine powder ) ) ( -LRB- ( ( ( ( adding ( liquid nitrogen ) ) periodically ) ( to ( ( prevent ( the tissue ) ) ( from thawing ) ) ) ) -RRB- ) ) ) ) ) ) . )
(ROOT (S (VP (VP (VB Pre-chill) (NP (DT a) (NN mortar))) (CC and) (VP (VB pestle) (PP (IN with) (NP (JJ liquid) (NN nitrogen)))) (CC and) (VP (VB grind) (NP (DT the) (NN plant) (NN tissue)) (PP (TO to) (NP (NP (DT a) (JJ fine) (NN powder)) (PRN (-LRB- -LRB-) (VP (VBG adding) (NP (JJ liquid) (NN nitrogen)) (ADVP (RB periodically)) (S (VP (TO to) (VP (VB prevent) (NP (DT the) (NN tissue)) (PP (IN from) (S (VP (VBG thawing)))))))) (-RRB- -RRB-)))))) (. .)))
Pre-chill a mortar and pestle with liquid nitrogen and grind the plant tissue to a fine powder (adding liquid nitrogen periodically to prevent the tissue from thawing).
(ROOT (S (NP (NN Ground) (NN tissue)) (VP (VBZ makes) (PRT (RP up)) (NP (NP (JJS most)) (PP (IN of) (NP (NP (DT the) (NN inside)) (PP (IN of) (NP (DT a) (NN plant))))))) (. .)))