Bell, Rogers & Zemurray Bros. v. Jenkins

“In order to let in evidence of a collateral agreement between the parties, such agreement must be consistent with the terms of the- writing; if the evidence tends to vary or contradict the terms of the written instrument, or to defeat its operation, it cannot be received.” 22 Corpus Juris, 1248.

But it is equally well settled that evidence of a collateral parol agreement about the same matter as that of the writing, but which does not vary or contradict the writing, is admissible upon proper pleading. Middleton v. Alabama Power Co., 196 Ala. 1, 71 So. 461; Roquemore v. Vulcan Iron Works, 151…