If the parties to a contract have not put all its terms in writing, parol evidence of the supplementary terms is admissible, not to vary, but to complete, the written contract.23 Thus, where a written contract for the sale of goods mentions the price, but is silent as to the terms of payment, the terms may be shown by parol evidence.24 And a subsequent agreement changing the terms of a written contract may be shown by parol evidence.25

Again, evidence may be given of an oral agreement collateral to the written contract, subjecting it to a term unexpressed in its contents; but such a term cannot be enforced if it is contrary to the tenor of the writing.26 "No doubt, as a rule of law, if parties enter into negotiations affecting the terms of a bargain, and afterwards reduce it into writing, verbal evidence will not be admitted to introduce additional terms into the, agreement; but, nevertheless, what is called a 'collateral agreement,' where the parties have entered into an agreement for a lease, or for any other deed under seal, may be made in consideration of one of the parties executing that deed, unless, of course, the stipulation contradicts the terms of the deed itself. I quite agree that an agreement of that kind is to be rather closely watched, and that we should not admit it without seeing clearly that it is substantially proved." 27

23Jervis v. Berridge, 8 Ch. App. 351; Potter v. Hopkins, 25 Wend. (N. Y.) 417; Batterman v. Pierce, 3 Hill (N. Y.) 171; Grierson v. Mason, 60 N. Y. 394; Holt v. Pie, 120 Pa. 425,. 14 Atl. 3S9; Lyon v. Lenon, 106 Ind. 507, 7 N. E. 311; Raynor v. Drew, 72 Cal. 307, 13 Pac. SG6; Reynolds v. Hassam, 56 Vt. 449; Coates v. Sangston, 5 Md. 121; Walter A. Wood Mach. Co. v. Gaertner, 55 Mich. 453, 21 N. W. 885; Lash v. Parlin, 78 Mo. 391; Bretto v. Levine, 50 Minn. 168, 52 N. W. 525; Mobile & M. Ry. Co. v. Jurey, 111 U. S. 584, 4 Sup. Ct. 566, 28 L. Ed. 527; Peabody v. Bement, 79 Mich. 47, 44 N. W. 416; Bank v. Cooper, 137 U. S. 473, 11 Sup. Ct. 160, 34 L. Ed. 759. See "Evidence," Dec. Dig. (Key-No.) § 441; Cent. Dig. §§ 1123-1163.

24Paul v. Owings, 32 Md. 402; Magill v. Stoddard, 70 Wis. 75, 35 N. W. 346. Where a contract specifies no time, parol evidence of a contemporaneous agreement as to time of payment is admissible. Horner v. Horner, 145 Pa. 258, 23 Atl. 441; Sivers v. Sivers, 97 Cal. 518, 32 Pac. 571. See "Evidence," Dec. Dig. (Key-No.) § Ml; Cent. Dig. §§ 1123-1163; "Sales," Cent. Dig. § 121.

25 Coe v. Hobby, 72 N. Y. 141, 147, 28 Am. Rep. 120; Kennebec Co. v. Augusta Ins. & B. Co., 6 Gray (Mass.) 204; Quigley v. De Haas, 98 Pa. 292; Smith v. Lilley, 17 R. I. 119, 20 Atl. 227; Stallings v. Gottschalk, 77 Md. 429, 26 Atl. 524; Bannon v. Aultman, 80 Wis. 307, 49 N. W. 9G7, 27 Am. St. Rep. 37; Worrell v. Forsyth, 141 111. 22, 30 N. E 673. See "Evidence," Dec. Dig. (Key-No.) § 445; Cent. Dig. §§ 2052-2065.

2«Lindley v. Lacy, 17 C. B. (N. S.) 578; Ayer v. Manufacturing Co., 147 Mass. 46, 16 N. E. 754; Chapin v. Dobson, 78 N. Y. 74, 34 Am. Rep. 512; Bonney v. Morrill, 57 Me. 368; Walker v. France, 112 Pa. 203, 5 Atl. 20S; Roberts v. Bonaparte, 73 Md. 191, 20 Atl. 918, 10 L. R. A. 689; Palmer v. Roath, 86 Mich. 602, 49 N. W. 590; Durkin v. Cobleigh, 156 Mass. 108, 30 N. E. 474, 17 L. R, A. 270, 32 Am. St. Rep. 436; Phoenix Pub. Co. v. Clothing Co., 54 Minn. 205, 55 N. W. 912; Keen v. Beckman, 66 Iowa, 672, 24 N. W. 270. See "Evidence," Dec. Dig. (Key-No.) § 442; Cent. Dig. §§ 1814-1897.