[ruby-talk:7069] Ruby/Tk question

I am new to the Ruby. I try to test the Ruby/Tk and enter the follow
program.

require 'tk'
root = TkRoot.new {
     title 'Frames'
}

[ 'raised', 'sunken', 'flat', 'ridge', 'groove', 'solid' ].each do |relief|
     f = TkFrame.new(root){
          borderwidth 2
          relief relief
          pack { side 'left'; padx  5; pady  5 }
     }

     TkLabel.new(f){
          text relief
          width 10
          pack { side 'left' }
     }
end

root.mainloop

I expected to see a row of labels. Instead I got a window with a column of
labels.
If I change the pack block to
pack( 'side' => 'left', 'padx' => 5, 'pady' => 5 )

The display change to a row of labels. Could anyone tell me what's the
difference between the two ways of calling pack. Thanks

Steve