<Tr> <Th> 37 </Th> <Td> </Td> <Td> "Time Has Come Today" </Td> <Td> Daniel Minahan </Td> <Td> Shonda Rhimes </Td> <Td> September 21, 2006 (2006 - 09 - 21) </Td> <Td> 25.41 </Td> </Tr> <Tr> <Td_colspan="7"> The interns of Seattle Grace Hospital help Izzie cope with the loss of her fiancé, Denny Duquette as well as her decision to quit the internship program . Meredith is uncertain what the future holds after she has sex with Derek and whether he is willing to leave Addison after a marriage of eleven years . Addison finds Meredith's panties in Derek's tux pocket, and realizes that he slept with Meredith . After spending the night in his office, Webber is confronted by his wife, Adele (Loretta Devine). She gives him an ultimatum, forcing him to decide between his career and his marriage . Addison and Alex treat a newborn baby who was found abandoned in a trash can, and they are faced with four minors who could be the mother . George seeks relationship advice from Derek after they are forced to stay under quarantine in the locker room, when Derek confesses his feeling towards Meredith . Bailey gets attached to a patient in isolation whose wife dies, and relives the moments when her husband's life was threatened . </Td> </Tr> <Tr> <Th> 38 </Th> <Td> </Td> <Td> "I Am a Tree" </Td> <Td> Jeff Melman </Td> <Td> Krista Vernoff </Td> <Td> September 28, 2006 (2006 - 09 - 28) </Td> <Td> 23.48 </Td> </Tr> <Tr> <Td_colspan="7"> Cristina makes a bad first impression on Burke's parents and is also surprised to find that he is a "mama's boy". Burke's mother believes that Cristina is too selfish and driven for her son, and is only trying to take advantage of his extensive knowledge of cardiothoracic surgery . Izzie uses baking to cope with her grieving, and bakes hundreds of muffins . After pinning Meredith's panties to a bulletin board, Addison takes a day off from the hospital and spends the day drinking . Due to Addison taking the day off, Bailey has Alex help her in the pit, and they're faced with a teenage patient who has been impaled on a tree branch . A brain tumor patient quizzes Meredith and Cristina over their respective relationships . Webber discovers that Callie has been living in the hospital and tells her she has to leave because of hospital policy . Bailey finds the panties on the bulletin board and loses it, demanding to know who they belong to . Callie sees Meredith's embarrassment and takes the blame, which in turn causes George to become jealous, fearing Callie might have cheated on him . A surgical patient lives what may be her last day to the fullest . Meredith must choose between Derek and Finn, and struggles coming to a decision . In the end she tells them both that she would like to try dating them both instead . </Td> </Tr>

When do meredith and derek start dating in season 3