The necessity of reliable local botanic data in solving the hay-fever problem has been frequently emphasized, and a number of field surveys have been made in which the common weeds that produce wind-borne pollen were observed and listed. At least one observer (Scheppegrell) has reported careful studies of atmospheric pollen over long periods. While field observation gives exact information as to the seasonal and geographic factors, it does not yield very satisfactory quantitative data. Exposing oil-coated plates to catch the air-borne pollens and making differential counts of them at regular intervals is a method that gives very valuable quantitative results, but it should be supported by careful field work. By using a combination of these two methods, we have been able to secure a large amount of satisfactory data on the distribution and abundance of the flora in Chicago; the time, duration and intensity of pollen production, and the relative