-Measurements of CO2 content of the atmosphere above Illinois forest and grassland soils indicate: CO2 concs. within 1 cm. above the soil surface are as high as 0.181%. CO2 concs. at 16 cm. above the soil are as high as 0.053%. Above 16 cm. CO2 concs. vary chiefly between 0.03 and 0.04%. CO2 concs. within 16 cm. of the soil surface are higher in forests than in grassland, probably because of more sluggish air movements in densely forested areas. It is suggested that mosses, liverworts, prostrate herbs, and other low-growing plants spend the major portion of their lives in an atmosphere considerably richer in CO2 than that available to taller plants.