How to paste a variable name into R `plot`

This seems like it should be pretty obvious, but I've tried substitute, bquote, expression, paste, and cat, with similar results (failure).

require(quantm开发者_Python百科od)
getSymbols("SAM")
thing = "SAM"
plot(SAM)      #this works fine
plot(thing)    #this does not

Encasing thing in xts(thing) and so on doesn't work either.

How about this:

plot(get(thing))  

Running thing = "SAM" simply assigns the character "SAM" to a variable named thing. R has no way to know (without you telling it) that you want it to connect the value of the character vector thing to a particular object in the environment (i.e. SAM). So get does the trick here.