How to install package effects

Dear all,

How to install function effects in R 3.1.2.?                         I got this:

 plot(effect("soil:volatile", model1))
Error in plot(effect("soil:volatile", model1)) :
  could not find function "effect"
Error in find.package(if (is.null(package)) loadedNamespaces() else package,  :
  there is no package called ''

Thank you very much,

Xavier