That from and after the passage and approval of this act [21-7-13, 21-7-14, 21-7-16 to 21-7-25 N.M. Stat. Ann.], all permanent funds thereafter derived from the sale or disposition of the lands held in trust for said university, shall be invested in bonds of the United States or of the state of New Mexico, the income from which shall likewise form a part of the pledged income for the payment of the principal and interest of said bonds issued by said board.