Withdrawals, exchanges of security

1. Securities pledged pursuant to this chapter may be withdrawn on application of the pledging depository institution, and as to securities pledged by a credit union upon approval of the public officer to whom the securities are pledged, if the deposit of securities is no longer necessary to comply with this chapter, or withdrawal is required for collection by virtue of maturity or exchange. The depository institution shall replace securities so withdrawn for collection or exchange. 2. In an exchange of deposited securities for new securities, the amount of security on deposit at any time shall not be decreased below that otherwise required by this chapter. 3. In the event of substitution, addition, or exchange of securities, the holder or custodian of the securities shall, on the same day, forward by regular mail to the public officer and the credit union, a receipt specifically describing and identifying both the substituted or additional securities. 4. The public officer which deposits public funds with a credit union shall require, if the market value of the securities deposited with or for the benefit of the officer falls below one hundred ten percent of the deposit liability to the public officer, the deposit of additional security to bring the total market value of the security to one hundred ten percent of the amount of public funds held by the credit union.