( First ( , ( ( the ( pollen grain ) ) ( ( is ( surrounded ( by ( ( a ( protective wall ) ) ( consisting ( of ( two ( layers ( , ( ( exine and ) intine ) ) ) ) ) ) ) ) ) ) . ) ) ) )
(ROOT (S (ADVP (RB First)) (, ,) (NP (DT the) (NN pollen) (NN grain)) (VP (VBZ is) (VP (VBN surrounded) (PP (IN by) (NP (NP (DT a) (JJ protective) (NN wall)) (VP (VBG consisting) (PP (IN of) (NP (CD two) (NNS layers) (, ,) (NN exine) (CC and) (NN intine)))))))) (. .)))
First, the pollen grain is surrounded by a protective wall consisting of two layers, exine and intine.
(ROOT (S (NP (NP (DT The) (NN pleura)) (SBAR (WHNP (WDT that)) (S (VP (VBZ surrounds) (NP (DT the) (NNS lungs)))))) (VP (VBZ consists) (PP (IN of) (NP (CD two) (NNS layers)))) (. .)))