( This ( ( is ( ( a type ) ( of ( sexual reproduction ) ) ) ) . ) )
(ROOT (S (NP (DT This)) (VP (VBZ is) (NP (NP (DT a) (NN type)) (PP (IN of) (NP (JJ sexual) (NN reproduction))))) (. .)))
This is a type  of sexual reproduction.
(ROOT (S (NP (JJ Sexual) (NN reproduction)) (ADVP (RB usually)) (VP (VBP occur) (PP (IN during) (NP (NP (NNS times)) (PP (IN of) (NP (JJ environmental) (NN stress)))))) (. .)))