Section 72. If any section or part of a section of this charter proves to be invalid or unconstitutional, the same shall not be held to invalidate or impair the validity, force or effect of any other section or part of a section of this charter unless it clearly appears that such other section or part of a section is wholly or necessarily dependent for its operation upon the section or part of section so held unconstitutional or invalid. If for any reason there is a failure to elect commissioners at the general election of November, 1917, an election for that purpose shall be held under the provisions of this charter on the first Tuesday of March, 1918, and the commissioners then elected shall immediately thereafter assume the duties of their office.