The root systems of potato plants (Solanum tuberosum L. var. Russet Burbank) treated with CO2 for 12 hours showed an increase in dry matter as early as 2 days after the treatment. When treated plants were allowed to grow for 3 to 6 weeks there was a substantial increase in tuberization. In addition, there was an increase in stolon length, number of tubers per stolon, and overall dry weight after the enrichment of the root zone with CO2. Plants treated with CO2 showed higher concentrations of malic and citric acids and of the cations Mg2+ and Ca2+. The effect of CO2 was more dramatic when CO2 was applied to the root zone than when it was applied to the shoots.