Many conflicting ideas have been expressed concerning osmotic pressure in plant cells. The purposes of this investigation were to determine the range of osmotic pressure in prairie plants and to ascertain, if possible, any correlation between osmotic pressure and certain ecological factors. Since the osmotic pressure of a solution is dependent upon the proportion of water and osmotically active substances, it may be concluded that either a decrease in the water content or an increase in osmotically active substances will have an identical effect, namely, an increase in the osmotic