The clerk shall accept for filing nominating petitions on official blanks containing the required number of signatures for candidates having those qualifications required for elective city officials by this charter. When petitions are filed by persons other than the person whose name appears thereon as a candidate, they may be accepted for filing only when accompanied by the written consent of the person in whose behalf the petition or petitions were circulated. The clerk shall, forthwith after the filing of a petition, determine the sufficiency of the signature on each petition filed, and if he finds that any petition does not contain the required number of legal signatures of registered electors, he shall immediately notify the candidate in writing of the insufficiency of his petition. Each petition which is found by the clerk to contain the required number of signatures of registered electors for candidates shall be marked `In Order', with the date thereof, and he shall so notify the candidate whose name appears thereon, in writing.