These alone could have valuable uses.
( These ( alone ( ( could ( have ( valuable uses ) ) ) . ) ) )
(ROOT (S (NP (DT These)) (ADVP (RB alone)) (VP (MD could) (VP (VB have) (NP (JJ valuable) (NNS uses)))) (. .)))
These by themselves could prove valueable. 
( ( These ( by themselves ) ) ( ( could ( prove valueable ) ) . ) )
(ROOT (S (NP (NP (DT These)) (PP (IN by) (NP (PRP themselves)))) (VP (MD could) (VP (VB prove) (NP (NN valueable)))) (. .)))