, the worst of tragedies can be fertile sources of humor 
(ROOT (S (, ,) (NP (NP (DT the) (JJS worst)) (PP (IN of) (NP (NNS tragedies)))) (VP (MD can) (VP (VB be) (NP (NP (JJ fertile) (NNS sources)) (PP (IN of) (NP (NN humor))))))))
(ROOT (S (, ) (NP (NP (DT ) (JJS )) (PP (IN ) (NP (NNS )))) (VP (MD ) (VP (VB ) (NP (NP (JJ ) (NNS )) (PP (IN ) (NP (NN ))))))))