ECOTONE CHARTS =225.= The contour lines of zones and consocies are of the utmost importance in recording the structure of vegetation. They do not permit such accuracy as do quadrats and transects, but this is hardly to be considered a disadvantage in view of the fact that ecotones are rarely sharply defined. In establishing the ecotones of zonation, the width and the length of the base, i. e., the area of excess or deficiency, or as much of it as is to be considered, are determined. This base may be road, ditch, pool, lake, or stream, or the peak or crest of a hill, ridge, or mountain. When the zonation is bilateral, meter tapes are run at right angles to the base, at proper intervals, and the points and the distances where the ecotones cross are noted. In the case of radial zones, the tapes are run in the four cardinal directions, and if the base be large, in the four intermediate ones also, the intersections being likewise noted. From the data thus obtained, the zones may be outlined with a fair degree of accuracy. If the series be an extensive one, it is charted to the scale of 100:1; in cases of small areas, however, the scale of 10:1 will give better results. Whenever the zones show clearly enough to warrant, a photograph is also taken. Water-content readings are of paramount importance in the interpretation of zones. Samples should be taken at all intersections, and the resulting values indicated at the corresponding points upon the chart. When the zones are broken up into alternating patches in consequence of asymmetry in the topography, the ecotones of the latter are traced in a similar fashion from the center of each as a base, the absolute position of which is ultimately determined with reference to the ecotone lines already established. THE MIGRATION CIRCLE =226. Purpose.= The migration circle is designed to record the invasion of species, since it operates outward from an individual or a group of plants as a center. As migration takes place to a certain degree in all directions, a circle is better adapted to the purpose than the quadrat. From the very nature of invasion, migration circles should always he permanent in order that the yearly advance may be accurately noted. Circles of this character are important aids in the study of any vegetation, except, perhaps, one that has practically become stabilized. Their great value, however, is found in succession, where it is necessary to trace the movement of new individuals away from the original invaders as centers of colonization.