All university and school lands which have been or may be forfeited by the non-payment of either principal or interest, and which have not been offered at public auction after forfeiture, before the same shall be subject to private entry, shall be re-offered for sale at public auction, and the minimum price of all portions or tracts upon which improvements shall have been made, shall be such as shall be determined by the commissioner in the manner hereinafter in this chapter provided.