Basic question on applying a function to each row of a dataframe

Hi,

I have a function foo(x,y) and a dataframe, DF,  comprised of two vectors, x 
& w,  as follows :

   x w
1  1 1
2  2 1
3  3 1
4  4 1

etc


I would like to apply the function foo to each 'pair' within DF e.g  
foo(1,1), foo(2,1), foo(3,1) etc

I have tried

apply(DF,foo)
apply(DF[,],foo)
apply(DF[DF$x,DF$w],foo)

However, none of the above worked. Can anyone help ?

Thanks in advance,
Peter