At the time and place mentioned in the notice, or at the time or times to which hearing upon such petition may be adjourned, the board of directors shall proceed to hear the petition and all objections thereto which are presented in writing, showing cause as aforesaid why the prayer of the petition should not be granted. The filing of such petition as aforesaid shall be deemed and taken as an assent by each and all of the petitioners to the exclusion from the district of the lands mentioned in the petition, or any part thereof.