In human society, density of population is marked by striking variations. With these are associated geographic, social, and economic differences. Among the plant populations of our fields occur gradations of spacing or density which, by broad analogy, suggest problems akin to those arising from density differences in human populations. It is necessary to do no more than walk the length of one of the drill rows in a field of young corn to appreciate the general situation. The facts are patent some five weeks after sowing when the emergence of the seedlings is almost completed. Side by side with a foot length of drill in which are thirty plants may be another foot with only three. Complete gaps of 2 feet or more are to be found in places: in others the plants are almost too numerous to count. In every field of corn, even at this early stage, the density or closeness of the plants in the drills is extremely irregular. As the season advances various influences induce irregular reductions in the number of plants. Vermin and disease take sporadic toll. Competition between plant and plant with death or effective disablement of the weaker has some effect. Its intensity at any point is mainly determined by the density or closeness of the plants. By May, for winter corn, a static condition has generally been reached. Plants living then are likely to contribute grain and straw to the harvest. Among these survivors are great differences in spacing. This may be readily appreciated by uplifting and counting the roots in sample 1-foot lengths of drill on a stubble field.