1. Where, on certiorari from a trial court, the certified copy of the certiorari bond is signed by one as agent for the surety named thereon, the authority of such agent must expressly appear (Taylor v. City of Atlanta, 84 Ga. App. 739, 67 S. E. 2d 143, and citations), as the validity of such bond is a condition precedent to obtaining a writ of certiorari. Hubert v. City of Thomasville, 18 Ga. App. 756 (90 S. E. 720), and the numerous citations.

2. Authority to execute a sealed instrument must itself be under seal. Overman v. Atkinson, 102 Ga. 750 (29 S. E. 758).

3. Where the certiorari bond is executed under seal by the principal and by the attorney in fact for the security, but it appears from the certified copy of such attorney’s power that it was not given and executed under seal, the certiorari bond is invalid (Taylor v. City of Atlanta, supra; Brooks v. Kiser, 69 Ga. 762; Willhelms v. Partoine, 72 Ga. 898); and it is not error for the superior court to dismiss a petition for certiorari where such defect as above indicated appears upon the face of the petition.

4. Nor is it error for the superior court to refuse to set aside and vacate such judgment dismissing the petition for certiorari upon the ground that the certified copy of the power of attorney was erroneous. Petitions for certiorari are not amendable. Carroll v. Inner Shoe Tire Co., 21 Ga. App. 397 (94 S. E. 643), and citations.

Judgment affirmed.