In the execution of any written instrument conveying, encumbering, or affecting real estate by a corporation that has adopted a corporate seal, the seal of such corporation may but need not be attached or affixed to such written instrument. [C51, §974; R60, §1823; C73, §2112; C97, §3068; S13, §3068; C24, 27, 31, 35, 39, § 10067; C46, 50, 54, 58, 62, 66, 71, 73, 75, 77, 79, 81, §558.2 ] 96 Acts, ch 1154, §1 Seals generally, §537A.1