At the end of the six-weeks period provided by section 735.20 of the Revised Code, the platting commissioner shall cause copies of the plat as finally adopted to be prepared and such monuments or marks as he thinks proper to be placed on the grounds. He shall deposit one copy, certified to by him, in the office of the county recorder, and another in the office of the city engineer, and such plan shall be deemed to be the regularly adopted plan for streets and alleys in such territory.