fun = function (parameter) {
result = get(paste0("dataframe","parameter"))
return(result) }

fun <- function(df, col){
  df[col]
}
fun(iris, "Sepal.Length")
    Sepal.Length
1            5.1
2            4.9
3            4.7
4            4.6
5            5.0
6            5.4
7            4.6
8            5.0
...