 The game is presented from a single , 2D perspective , and revolves around Robbie the Robot 's objective to defend his plant from interstellar space slugs . The plant grows from a pot at the bottom centre of the screen , and spray cans containing three different pesticides are located on ledges on each side of the screen . Bonus items such as fertiliser and spades appear on unoccupied ledges which will increase both the players score and the plant 's growth rate . 
