All securities purchased or held on behalf of said funds, shall be held and disbursed through the state treasury and shall be in the physical custody of the state treasurer, who may deposit with the fiscal agent of the state, or with a state depository, such of said securities as he or she shall consider advisable to be held in safekeeping by said agent or bank for collection of principal and interest, or of the proceeds of sale thereof.
RCW 43.84.041