Sinking funds of school district; investment in warrants; limitation; direction to treasurer

The school board of any school district in this state is authorized to direct the legal custodian of any of its sinking funds to invest such sinking funds in the warrants of such school district in like manner as hereinbefore provided for. The investment of such school district sinking fund under this section shall be limited to the warrants of its own issue. Upon such direction of the school board, the custodian of such sinking funds shall proceed to take up the warrants of such school district as herein provided for.