The quadrat constitutes the initial concept from which all the methods have grown. In itself, it has given rise to a variety of quadrats applicable to the most fundamental problems of vegetation. From it have come, on the one hand, the migration circle, and on the other, the transect. The latter in turn has yielded the ecotone chart, and the layer chart. All of these are based upon direct and detailed contact with vegetation itself, and permit accurate recording of all the results obtained. QUADRATS =199. Uses.= In its simplest form, the quadrat, as the name implies, is merely a square area of varying size marked off in a formation for the purpose of obtaining accurate information as to the number and grouping of the plants present. As indicated above, it was first used for determining the abundance of the various species of a formation. This made it possible to ascertain the relative rank of the species of layers and formations, and enabled one for the first time to gain some idea of the minute structure of a bit of vegetation. The results were at once applied to the task of establishing a numerical basis for abundance, and of working out a new system of abundance to correspond. The quadrat method was also used to determine the character of seasonal aspects, and to yield a knowledge of the exact differences in diverse areas of the same formation. Incidentally, the determinations of abundance were made the basis of an actual census of certain alpine formations. This, while it was extremely interesting to find that a square mile of alpine meadow contained approximately 1,500,000,000 plants, was confessedly destitute of ecological value. The most important applications of the quadrat idea were made by Clements[21] in the chart, the permanent and the denuded quadrats. The development of these was due to the fact that zones or formations permit of comparison upon floristic as well as physical grounds, and that a detailed record of their structure is necessary for this purpose. Similar comparisons are necessary for the consocies, zones, and patches of the same formation, and the quadrat becomes an indispensable means for studying alternation and zonation. For the investigation of invasion year by year, and especially for succession, the method of permanent quadrats is imperative, and the denuded quadrat an invaluable aid. Changes, which would otherwise be incompletely observed and imperfectly recorded, are followed in the minutest detail and recorded with perfect accuracy.