Bonds may be issued as (i) coupon bonds payable to bearer, (ii) coupon bonds registrable as to principal only or as to both principal and interest, or (iii) bonds without coupons registered as to both principal and interest. Each issuing unit may appoint or designate a bond registrar who shall be charged with the duty of attending to the registration and the registration of transfer of bonds. (1917, c. 138, s. 29; 1919, c. 178, s. 3(29); C.S., s. 2955; 1921, c. 8, s. 1; Ex. Sess. 1921, c. 106, s. 1; 1927, c. 81, s. 36; 1971, c. 780, s. 1; 1973, c. 494, s. 22.)