Stagy, C. J.

This is another instance of a father coming to tbe rescue of bis son by promising to pay tbe latter’s note if not paid at maturity. A guaranty of payment is an absolute promise to pay tbe debt at maturity if not paid by tbe principal debtor. S. v. Bank, 193 N. C., 524, 137 S. E., 593; Cowan v. Roberts, 134 N. C., 415, 46 S. E., 979. But as a consideration for tbe guaranty plaintiff agreed to furnish tbe son, on open account, fertilizer to make bis crop for tbe year 1929. This was tbe sine qua non of the father’s guaranty, and tbe plaintiff has failed to comply with its part of tbe agreement.

Tbe note in suit is made payable to tbe American Agricultural Chemical Company, or order; and it is always open, as between tbe original parties to a contract, upon proper plea, to show a total failure of consideration. Swift & Co. v. Aydlett, 192 N. C., 330, 135 S. E., 141; Pate v. Gaitley, 183 N. C., 262, 111 S. E., 339.

Tbe admission of this character of evidence is not at variance with tbe rule against changing, contradicting or adding to tbe terms of a written instrument by parol, nor is it prohibited by tbe statute of frauds. Harper v. Harper, 92 N. C., 300; 3 R. C. L., 139.

Want of consideration is one of tbe exceptions to tbe rule tbat parol evidence of an oral agreement, alleged to have been made at tbe time of tbe drawing, making or endorsing of a bill or note, is not competent to vary, qualify or contradict, add to or subtract from tbe absolute terms of a written instrument. 2 Parsons Notes and Bills, 501.

Tbe rejected testimony of tbe defendant tending to establish tbe affirmative of tbe 2d and- 3d issues was competent under tbe exception. Carrington v. Waff, 112 N. C., 115, 16 S. E., 1008.

New trial.