Crude Oil Prices and VGENX Vanguard Energy

[rothnroll]

Crude oil is back below $40
http://finance.yahoo.com/news/crude-oil-tumbling-again-worst-145343123.html
It was 50 dollars in June
And dropped 22% in July.
Wouldn't this cause the price of Vanguard Energy VGENX to decrease/plummet?
Which it hasn't.
Can anyone explain that to me in childlike terms?

Thanks!