Article IV, § 18 — Amendment of statutes

No law shall be revised or amended, or the provisions thereof extended by reference to its title only; but each section thereof as revised, amended or extended shall be set out in full. Notwithstanding the foregoing or any other provision of this constitution, the legislature, in any law imposing a tax or taxes, may define the amount on, in respect to or by which such tax or taxes are imposed or measured, by reference to any provision of the laws of the United States as the same may be or become effective at any time or from time to time, and may prescribe exceptions or modifications to any such provision.