The Legislature, in compliance with the provisions of this Constitution, shall prior to the first day of July, one thousand nine hundred and forty-nine, and may from time to time thereafter, allocate by law the executive and administrative offices, departments and instrumentalities of the State government among and within the principal departments. If such allocation shall not have been completed within the time limited, the Governor shall call a special session of the Legislature to which he shall submit a plan or plans for consideration to complete such allocation; and no other matters shall be considered at such session.