If a director of a subsidiary bank--
         (a) is, or has become, subject to any of the disqualifications mentioned in section 27; or
         (b) resigns his office by giving notice in writing under his hand, in the case of a nominated director to the State Bank, and in the case of an elected director to the Board of Director of the subsidiary bank, and his registration is accepted; or
         (c) is absent without leave of the Board of Directors for more than three consecutive meetings thereof;
his seat on the Board of Directors shall thereupon become vacant:
     Provided that nothing in clause (b) or clause (c) shall apply to a director referred to in clause (b) of sub-section (1) of section 25 or to a director, being an officer of the State Bank, nominated under clause (c) or to a director, being an officer of the Central Government nominated under clause (e) of that sub-section.