Mich. Comp. Laws § 444.108

Sec. 8. Nothing in this act shall be construed as prohibiting or preventing warehousemen from mingling in common bins, grains or beans or seeds of the same grade, issuing certificates or receipts therefor, and drawing out and shipping said grain, beans or seeds from said bins: Provided, That a sufficient quantity of such grain or seeds shall be retained and kept in said bins to represent and satisfy all outstanding receipts or certificates.