=203. Locating quadrats.= In staking a quadrat, the end tapes are invariably placed so that the numbers read from left to right, and the side tapes so that they read down. In mapping, a fifth tape is stretched parallel to the top, and as each decimeter strip is marked, the outer tape is shifted to delimit the new strip. Indeed, the side tapes can be placed alone, and the plotting tapes moved down one at a time as the mapping proceeds, but it is usually more satisfactory to locate the quadrat exactly and to square it first, a task most easily done by enclosing the whole quadrat, and then using a fifth tape. In the case of list quadrats in open vegetation, the measuring strip is unnecessary, but as a rule it facilitates counting, as well as mapping. [Illustration: Fig. 50. Mapping a major quadrat on Mount Garfield at 3,600 m.] _The List Quadrat_ =204. Description.= This, as the simplest form of quadrat, is employed primarily to ascertain the abundance of species in a formation or during a particular aspect of it. Since this can be obtained readily from the chart, the list quadrat has fallen more and more into disuse, except where it is desired to determine abundance alone, or to aid in deciding whether a chart is really representative. The size depends almost wholly upon the nature of the vegetation. When the number of trees is to be determined, a quadrat of 10 or 50 meters is necessary. In ordinary herbaceous formations, the usual size is 2 meters, while the meter quadrat is used when the plants are especially small and crowded, as in alpine meadows. The location of the quadrat is based upon the general rule, but since its especial task is the determination of the greatest variable in vegetation, viz., number, it is necessary to use more quadrats, and to place them in areas which show the greatest differences in the mixture of species. For example, it was found that a half dozen list quadrats, when carefully located in the prairie formation, gave results almost identical with those obtainable from a larger number. With a little experience, the various degrees of mixture can be picked out superficially, and the corresponding number of quadrats established. If a single list quadrat is to be made for a formation or station, such a time should be selected as will make it possible to cover the greatest number of plants. Fortunately, this usually falls near the middle of the summer, when the remains of spring plants are still in evidence, and the autumn ones are sufficiently developed to be recognizable. In taking the census of different aspects, the quadrat should be made as near the middle of the period as is possible.