( ( ( Composed mainly ) ( of ( epithelial cells ) ) ) ( , ( glands ( ( are ( considered ( ( a type ) ( of ( epithelial tissue ) ) ) ) ) . ) ) ) )
(ROOT (S (S (VP (VBN Composed) (ADVP (RB mainly)) (PP (IN of) (NP (JJ epithelial) (NNS cells))))) (, ,) (NP (NNS glands)) (VP (VBP are) (VP (VBN considered) (NP (NP (DT a) (NN type)) (PP (IN of) (NP (JJ epithelial) (NN tissue)))))) (. .)))
Composed mainly of epithelial cells, glands are considered a type of epithelial tissue.
(ROOT (S (NP (NNP Epithelial) (. ?) (NNP tissue)) (VP (VBZ consists) (PP (IN of) (NP (NP (NNS cells)) (SBAR (WHNP (WHNP (WDT that) (NN cover)) (NP (JJ inner) (CC and) (JJ outer) (NN body))) (S (VP (VBZ surfaces))))))) (. .)))