Luis Buñuel’s black comedy Tristana, while taken from Benito Pérez Galdós’s 1892 novel, reflects twentieth-century political concerns, and owes something also to Alfred Hitchcock’s Vertigo (1958). It is less an allegory of Spain’s modern political history than a mismatch of humanity and politics, where each side is riddled with ambiguity. Perhaps Buñuel means to suggest that Spanish history itself contains shards of allegory.
Tristana is an orphaned innocent when guardian Don Lope (Fernando Rey, marvelous) seduces her, his virtuous socialist promptings as unable to curb his sexual appetite as erase his aristocratic demeanor. The two become lovers, with Don Lope instructing Tristana she is entirely free—a way by which he wards off facing the implications of his having impressed and impounded her into his sordid sexual service. In time, Tristana loses her heart to a boy whom she marries, loses a tumorous leg and with it, apparently, her human heart, abandons her spouse, and returns to Don Lope, who is frail now, to torment him and wreak vengeance. She is the guardian now.
Buñuel brilliantly recycles the detached leg from the wax version of Lavinia in The Criminal Life of Archibaldo de la Cruz (1955); but in Tristana there isn’t this remove of a mannequin. It is the actual Tristana whose artificial leg we offhandedly see reclining on her bed, enrobed in a seductive aura, and more powerfully erotic than anything else in Buñuel’s œuvre. Don Lope’s attraction to Tristana was no more connected to the innocent schoolgirl than this artificial leg is; she was always, for him, an object upon which he projected the surfeit of his sexual feelings. Their relationship, including her rejection of him, stirred up something else in Tristana: tormenting guilt. She is the monster they have both made of her.
Dennis Grunes 
One correction in your posting, she did NOT marry the artist she ran away with.