In stanza 1, what happens to an anger that is not settled?

"A Poison Tree" is a poem by William Blake that is concerned with the nature of anger and its capacity to fester if not dealt with and dispersed. In the first stanza of the poem, the speaker indicates that when angry with a friend, "speaking" the wrath brought it to a close, the issue having been handled. When angry with a foe, however, "I told it not, my wrath did grow." Where the speaker has not felt able or willing to express his feelings of anger to the person who has angered him, he feels that failure to vent the anger simply causes it to become toxic, growing to greater and greater proportions like the eponymous poison tree. The longer this situation endures, the more the angered party nurtures the tree of his anger, keeping his silence and watering the plant to encourage its growth.