could someone explain the difference to me

[ilk]

Hi all could someone explain why is this happening?

Ive got a first piece of code:

Private Function Clone2(ByVal s As String) As String
        clone2 = s
End Function

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

dim s as string
dim ss as string

s = "asdf"
ss = clone2(s)
ss = "zxcv"
    End Sub

Which happily makes value of s = "asdf" and value of ss = "zxcv"

now have a look at another peice of code

Public Function Clone2(ByVal tn As TreeNode) As TreeNode
        clone2 = tn
    End Function

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

dim tn as new treenode()
dim tnn as treenode

tn.text = "asdf"
tnn = clone2(tn)
tnn.text = "zxcv"
    End Sub

Which makes tn.text and tnn.text = "zxcv"


Why????