Puck appears, Act II, scene ii
Excerpt from the scene summary: Puck appears, carrying the flower whose juice will serve as the love potion. Oberon takes the flower and says that he knows of a fragrant stream bank surrounded with flowers where Titania often sleeps. Before hurrying away to anoint Titania’s eyelids with the flower’s juice, Oberon orders Puck to look for an Athenian youth being pursued by a lady and to put some of the juice on the disdainful youth’s eyelids, so that when he wakes he will fall in love with the lady. He informs Puck that he will know the youth by his Athenian garb. Puck agrees to carry out his master’s wishes.
Link to the full summary and information source: SparkNotes, "Midsummer Night's Dream" - http://www.sparknotes.com/shakespeare/msnd/section4.rhtml
Image Source: Circulating Collection, Print and Picture Collection, Free Library of Philadelphia. Subject: "Midsummer Night's Dream" -- Shakespeare.