Amanda, Tom and Laura's mother is both a symbol and an image in the play.  Symbolically, she represents a time gone by, a genteel time, when a lady was called upon by her gentleman callers and her future was secured through a prosperous marriage. 

 Laura, on the other hand has no such environment on which to rely for her future.  Amanda, between her behaviors, attitudes and her southern charm, keeps the old south alive in the play, so that the reader is constantly imagining what her life was like.  On the other hand, Amanda's image, of a washed out old debutante who is stuck in the past reflects the hopelessness of the situation in the family.

Tom keeps the image of his missing father alive through his attitude toward Amanda. Tom is a symbolic stand in for his long gone father.  Amanda, in the end, chases Tom away too. 

Laura, like Amanda will end up alone.  After Laura has her romantic interlude with her old high school friend, Jim, and he leaves abruptly because he is getting married.  It is easy to imagine that Laura will never leave the house again.

The dreary apartment reflects the melancholy of the lives of the characters.  The darkness that Tom leaves his mother and sister in is both figurative and literal.  They are left in physical darkness as they face the darkness of their uncertain future.  A future that at the end of the play consists of no income, no job and no prospects.   

There are many symbols used in the play. In fact, the play is so rich that it overflows with them. The core symbol is, of course, the glass menagerie that gives the play its title—Laura's precious glass animals. When Tom breaks one, it represents not just an accident but a shattering of part of her innocence. When the typewriter is on stage, it represents Laura's failed attempt to make a life out in the world via business college. Jim's accidental nickname for Laura—Blue Roses—is something that is never found naturally out in the world, and would only exist in a hothouse situation; the same is true of Laura, and so it becomes a symbol of her. The "gentleman callers" Amanda remembers were real, but they also symbolize a lost age. The fire escape is a literal place; it really exists for their apartment. However, even the family sees it as a symbolic substitute for a porch, and Tom uses it as an escape from his life. When the lights go out, it happens on a literal level because Tom forgot to pay the bill, but it symbolizes the growing darkness in their lives and how distant Tom is from reality.

Greg

What symbolism is present in the play The Glass Menagerie?

Besides the obvious symbolism of the menagerie itself (especially the unicorn’s losing its horn), Williams has made liberal use of symbolism in the dialogue and in the details of the Wingfield household.  For example “(My father) fell in love with long distance” is symbolic of his having deserted the Wingfield family (it can be argued that the very name of the family is symbolic).  For Tom, the fire escape balcony where he goes to dream is symbolic of the ship deck of a boat (he ends up in the Coast Guard) from where he can see the world and find adventures (and the music drifting up to him is symbolic of the romantic life just out of reach).  The movies he goes to are also symbolic of his desire to get out of his real-life situation.  The Gentleman Caller calls Laura “Blue Roses”, transforming symbolically her disease, pleurisy, into something unique and beautiful.  The whole play works this way; what appears as a normal family is actually a symbolic setting for being trapped in the romance of the past (Amanda’s flaw), unable to escape it and join the real world of the present. To address the unicorn symbolism, when Tom swings his jacket (symbolic of his unrest at being trapped there, and of his anguish to depart on an adventure of his own) and knocks the horn off the unicorn, Williams has transformed the mythic creature from a make-believe Romantic world into a real-life horse, a creature of the real world.