Yes, we’ve got some flower stuff going on here. Amanda always talks about jonquils when referring to her past, when she herself was a pretty little Southern Belle surrounded by dozens of gentlemen callers. Jonquils are a type of Narcissus, which is named of course from Greek Mythology and has to do with vanity, or narcissism. Interesting. Also, and we may be getting totally out of hand here, but jonquils are the same thing that we Americans call daffodils, and e.e. cummings, who is referenced to already twice in the play, wrote a poem about daffodils that also discusses roses. Not that that means anything. Back to business: for Amanda, the flowers are reminiscent of the past and signify what she wants for her daughter.
So Laura counters with blue roses. Jim’s old nickname for Laura, "Blue Roses," comes to represent Laura’s unique and individual self, a self that Jim and only Jim recognizes. Blue roses have this sort of mythical significance of being mysterious, or impossible to come by, which makes sense when you look at Jim’s description of Laura as a one-in-a-million girl.