Quadrats have been denuded in the fall after the majority of the plants have completed their growth. This is largely owing to the fact that other field work is less pressing at this time. Denudation can be done as well in the spring, though the invasion will be slower in this case, since the seeds which have accumulated will be partly or entirely removed. During the first season the denuded quadrat should be mapped every month, and, if the invasion be rapid, photographed also. In open formations, especially those of a xerophytic nature, a single chart and photograph made at the end of the season are sufficient. In a few cases of this sort, indeed, no invaders have appeared until the second year. Beginning with the second season, a single record taken near the close of the growing period will suffice. Denuded quadrats are labeled, dated, and filed exactly as other permanent quadrats, but it should be noted that the first member of the chart and photograph series is that which records the original vegetation of the area denuded. =215. Physical factors.= When denuded quadrats are single, their physical factors must be observed in the usual way. If they are associated with permanent ones, the ordinary readings are made for the latter, and those factors which are affected by exposing the soil are alone taken for the denuded area. These are the water-content, soil and surface temperatures, and in some stations at least the humidity near the surface. As everywhere, water-content is the most important, but the temperature at or near the surface has a marked effect upon germination. Because of its bearing upon the latter, the surface water-content is usually determined also. This has been done by taking a surface sample 2 inches square and 1 inch deep. Denuded quadrats naturally show considerable differences from year to year as the action of the invaders becomes more pronounced. To this fact is due much of their value as aids in interpreting succession. _Aquatic Quadrats_ =216. Scope.= The preceding discussion of quadrat methods is based wholly upon their use in terrestrial formations. Wet meadow and dry bog are the wettest places in which quadrats have been used. It is clear, however, that with certain necessary modifications, quadrats can be used as successfully, though not as conveniently, in many water formations as in land ones. The tapes need to be raised above the surface of the water by longer stakes, and photographs often taken from a boat, but otherwise the usual methods apply, at any rate for bogs and shallow bodies of water. In lakes or streams the tapes might be attached to buoys or floats. The determination of factors is made as usual. Permanent quadrats are feasible in many cases at least, and denuded quadrats are not altogether impossible. TRANSECTS