An "ashplant" is a walking stick fashioned from a sapling that has been cut off below the surface of the soil. The main root of many ash saplings takes a horizontal bend for several inches, several inches below the surface, before continuing its downward path, and such a sapling supplies a natural handle when the stick is inverted (personal communication from Don Gifford). Stephen may have begun carrying his for protection against dogs, but he thinks of it as also possessing various kinds of magical power.
In James Joyce's Disunited Kingdom and the Irish Dimension (Gill and Macmillan, 1976), John Garvin devotes a chapter (pp. 27-32) to the ashplant. His information about its origins in an uprooted sapling agrees with Gifford's, but he adds that it is seasoned in a chimney and filled with molten lead. Garvin speculates that Joyce acquired his ashplant during one of his visits to Mullingar and surrounding parts of Westmeath in 1900 and 1901.
Stephen’s ashplant has a “ferrule,” a metal ring or cap placed at the end of the shaft to keep it from splitting or wearing down. In Telemachus the “squealing” of the metal scraping against stone makes him think of a “familiar,” the supernatural animal-like spirit which attends a magician. He imagines this little spirit calling "Steeeeeeeeeeeephen!" as he walks along dragging the stick behind him.
At the beginning of Proteus, Stephen thinks, "My ash sword hangs at my side." Later in the chapter, he lifts his ashplant by its “hilt” as if it were a sword, “lunging with it softly.” This playful action anticipates a climactic action in Circe, when Stephen cries, “Nothung!”—the name of the magic sword in Wagner’s Ring cycle—and raises it over his head with both hands to smash the chandelier in the brothel. Gifford notes that in the second of the four operas in the cycle, Die Walküre, the god Wotan has planted this sword “in the heart of a giant ash tree” (emphasis added). Siegfried’s father Siegmund pulls the sword from the tree, and in the final opera of the cycle, Die Götterdämmerung, Siegfried unwittingly uses the magic of Nothung to bring about the Twilight of the Gods.
The Wagnerian magical subtext empowers Stephen. When he smashes the chandelier he is violently resisting his mother’s fiendish call to repent and return to God’s grace. The ruin of the lamp makes him think of the “ruin of all space” and time: the destruction of the divinely constituted order which he has been contemplating ever since Nestor.
In Proteus Stephen calls his stick "my augur's rod of ash," linking it with another kind of magical power. Just as the shape of the stick has allowed him to think of it as a sword with a hilt, so now it becomes a lituus, a staff with one curved end that Roman priests used to consecrate a sector of the sky before reading the appearance of birds for omens. The priests' staffs were elaborately curved, like the crozier of a Christian bishop, but earlier Etruscan brass horns, also called litui, had shapes more exactly approximating Stephen's walking stick. Apparently, the name originally referred to a shepherd's crook.
Joyce thought of his own ashplant as distinctively Irish, and it has been suggested that Stephen's stick should also be seen as embodying the prophetic power of the ancient Irish filí, or bards.