I saw a black branch with blood that kept drippin'I've always been intrigued by the possibility that Dylan was influenced by a scene in Dante's Inferno when writing this line. In the seventh circle (Canto 13), Virgil leads Dante through the Wood of Suicides, where Dante breaks off a twig from one of the trees:
Then I stretched my hand a little forward and plucked a branchlet from a great thorn-bush, and its trunk cried out, "Why dost thou rend me?" When it had become dark with blood it began again to cry, "Why dost thou tear me? hast thou not any spirit of pity? Men we were, and now we are become stocks; truly thy hand ought to be more pitiful had we been the souls of serpents." (tr. Charles Eliot Norton)As all the commentators note, Dante in turn is influenced by a scene in Virgil's Aeneid (Book 3):
There, while I went to crop the sylvan scenes,
And shade our altar with their leafy greens,
I pull'd a plant- with horror I relate
A prodigy so strange and full of fate.
The rooted fibers rose, and from the wound
Black bloody drops distill'd upon the ground.
(John Dryden translation)
In the 16th century, Spenser used the same image in The Faerie Queene:
And thinking of those braunches greene to frame
A girlond for her dainty forehead fit,
He pluckt a bough; out of whose rift there came
Small drops of gory bloud, that trickled downe the same.
In all these cases the tree is in fact a human being; but only in Dante's case is the arborification of the human a punishment for a specific sin, namely suicide. (The human trees in Virgil and Spenser just happened to fall afoul of the wrong god or witch.) This fits well in the context of Dylan's song, where the images in the catalog all have some kind of moral resonance.
And we now know that Dylan in the early '60's was reading The Inferno. He mentions it in his memoir Chronicles Volume One.
Still, even after all this source hunting, I remain uncertain. It recently struck me that an equally good source (if we must have a source) is the anti-lynching protest song "Strange Fruit" made famous by Billie Holliday:
Southern trees bear strange fruit,
Blood on the leaves and blood at the root
"Strange Fruit" was written by a Jewish songwriter (Abel Meeropol) under a different name (Lewis Allan). Meeropol was also known for having adopted the children of Julius and Ethel Rosenberg after their execution. It seems likely to me that Dylan, who was active in New York leftist circles in the early '60's, might have been attracted to this song for many reasons. ("Strange Fruit" is also mentioned in Chronicles.)