Friar Lawrence's Cell
The scene opens with Friar Lawrence gathering weeds, herbs, and flowers. As he does this, he explains in detail each one; this shows his deep and thorough knowledge of the plants and their properties: "Within the infant rind of this weak flower/Poison hath residence, and medicine power,/For this, being smelt, with that part cheers each part;/Being tasted, slays all senses within the heart." (Lines 23-26)
In showing the good and bad properties of these plants, this can also be seen as a symbol for men, and their abilitites to be good as well as evil.
The beginning of this scene could also be an instance of foreshadowing, in that, Friar Lawrence's knowledge of plants will play a part in attempting to help Romeo and Juliet be together. In addition, the symbolism of the flowers lends itself to foreshadowing the actions of specific characters as the play progresses.