Texas Natural Resources Code - NAT RES § 161.130. Constitutional Appropriations

(a) If during the existence of the fund or during the time general obligation bonds are payable from the fund the board determines that there will not be sufficient money in the fund during the following biennium available to pay principal of or interest on the bonds that are to come due and to be paid from the fund during that biennium, the comptroller shall transfer to the fund the first money coming into the State Treasury not otherwise appropriated by the constitution in amounts sufficient to pay the obligations.

(b) The money appropriated shall be used to pay the obligations only if at the time the principal or interest actually become due there is not sufficient money in the fund available to pay the amount due.