Missouri Constitution – Article II – The Distribution of Powers
Three departments of government-separation of powers
Section 1. The powers of government shall be divided into three distinct departments–the legislative, executive and judicial–each of which shall be confided to a separate magistracy, and no person, or collection of persons, charged with the exercise of powers properly belonging to one of those departments, shall exercise any power properly belonging to either of the others, except in the instances in this constitution expressly directed or permitted.
Source: Const. of 1875, Art. III.