A national atmospheric pollen survey is the natural outgrowth of the rapidly increasing interest in local pollen research. Such an investigation should naturally begin with ragweed, on account of its unquestioned preeminence as a national allergic nuisance. It is my purpose in this paper, not only to picture the conditions that annually confront fall hay-fever sufferers of the United States, but to present in a simple manner the effect of the more important factors influencing the production and distribution of ragweed pollen. Since the work is to be repeated during 1930, little attempt will be made to evaluate these various factors. Even where correlations are plotted, only the most obvious conclusions are drawn. Suggested explanations must in most cases wait for further confirmation.
In comparative studies1 conducted by private local cooperation it has been impossible to standardize the technic of air "sampling." This difficulty was practically solved in this