The board of trustees shall be trustees of the several funds of the system and may invest and reinvest such funds as authorized by this part and by law from time to time provided. Subject to the terms, conditions, limitations and restrictions of this part and by law from time to time provided, the trustees may hold, purchase, sell, assign, transfer or dispose of any of the securities and investments in which any of the funds created herein shall have been invested, as well as of the proceeds of the investments and any moneys belonging to the funds.