Missouri Constitution
Article IV - Executive Department
Section 26 Power of partial veto of appropriation bills—procedure—limitations.

The governor may object to one or more items or portions of items of appropriation of money in any bill presented to him, while approving other portions of the bill. On signing it he shall append to the bill a statement of the items or portions of items to which he objects and such items or portions shall not take effect. If the general assembly be in session he shall transmit to the house in which the bill originated a copy of the statement, and the items or portions objected to shall be reconsidered separately. If it be not in session he shall transmit the bill within forty-five days to the office of the secretary of state with his approval or reasons for disapproval. The governor shall not reduce any appropriation for free public schools, or for the payment of principal and interest on the public debt.

Source: Const. of 1875, Art. IV, Sec. 13.