Chapter 3. 65.6: “In Canto XIII of the Inferno, Dante and Virgil enter a pathless wood full of withered trees. Hearing a mournful wailing but seeing no one, the poet stops and is advised by Virgil to break off a twig from one of the trees. Dante does so; the tree becomes dark with blood and begins to cry: ‘Perché mi scerpi? / non hai tu spirto di pietade alcuno?’ (‘Why do you tear me? / Have you no spirit of pity?’). The trees are the suicides, those who have wantonly destroyed their lives and poisoned their souls and are therefore fixed for eternity in barren sterility. [. . .]”

Chapter 3. 65.7: “In Mexico, figures of Christ or the Virgin Mary are common features of house or garden walls as reminders of the suffering Christ assumed on behalf of all. The words also evoke the suffering figure of Faustus: the earlier ‘Regard’ recalls his hellish fall, but the emphasis here, as with the echoes of Eliot and Dante above, is on blood and sorrow and compassion. Faustus, in distress and anguish, cannot look up to heaven for the mercy that is there; one drop of Christ’s blood would save his soul, but he cannot avoid despair. Like Faustus, the Consul is unable to ask for relief, even though it is so immediately at hand. In an early draft [UBC 29-8, 1] Lowry was more explicit: ‘You have always secretly longed, like Christ, even like your own brother, to die.'” [. . .]    — The Malcolm Lowry Project: Under The Volcano, June 2012.

See these and many more Dante-related annotations to Under the Volcano at the hypertext resource the Malcolm Lowry Project, sponsored by University of Otago (NZ).