Query regarding "Call" statement

[anupam4j]

The following piece of code gives an output value 10 :

Code:

Function FinalVal( ByRef var )
    var = var + 1
End Function

Dim x: x = 10
FinalVal(x)
MsgBox x

'--------------------------

But the following code gives an output value 11 :

Code:

Function FinalVal( ByRef var )
    var = var + 1
End Function

Dim x: x = 10
call FinalVal(x)

MsgBox x

'----------------------------

Its clear that the use of the "Call" statement is the reason behind the difference in the output.
But why does that happen?