( ( Describe ( ( the ( rod ( and ( cone cells ) ) ) ) ( of ( ( ( the retina ) and ) ( their pigments ) ) ) ) ) . )
(ROOT (S (VP (VB Describe) (NP (NP (DT the) (NN rod) (CC and) (NN cone) (NNS cells)) (PP (IN of) (NP (NP (DT the) (NN retina)) (CC and) (NP (PRP$ their) (NNS pigments)))))) (. .)))
Describe the rod and cone cells of the retina and their pigments.
(ROOT (S (NP (NP (DT The) (JJ light-sensing) (NNS cells)) (PP (IN in) (NP (DT the) (NN retina)))) (VP (VBP are) (VP (VBN called) (NP (NNS rods) (CC and) (NNS cones)))) (. .)))