( It ( ( ( ( is ( virtually drought-proof ) ) and ) ( has ( ( no ( critical period ) ) ( when ( it ( must ( receive rain ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (PRP It)) (VP (VP (VBZ is) (ADJP (RB virtually) (JJ drought-proof))) (CC and) (VP (VBZ has) (NP (NP (DT no) (JJ critical) (NN period)) (SBAR (WHADVP (WRB when)) (S (NP (PRP it)) (VP (MD must) (VP (VB receive) (NP (NN rain))))))))) (. .)))
It is virtually drought-proof and has no critical period when it must receive rain.
(ROOT (S (NP (NNS Droughts)) (VP (VBZ occurs) (SBAR (WHADVP (WRB when)) (S (NP (EX there)) (VP (VBZ is) (ADJP (JJ little) (PP (TO to) (NP (NP (DT no) (NN rain)) (PP (IN in) (NP (NP (DT a) (NN period)) (PP (IN of) (NP (NN time)))))))))))) (. .)))