=196. Water-content series.= An account of the experiments which have been carried on for four generations with _Ranunculus sceleratus_ will serve to show the application of culture methods to the origin of new forms in response to varying water-content. This species was chosen because it grows readily in the planthouse, is plastic, and, since it is naturally amphibious, permits of much modification in both directions. The smallest amount of water per day under which the seedlings would grow was found to be 25 cc. This was taken as one extreme for the series, and deep water in which the plant could be submerged as the other. An arbitrary series was tentatively made as follows: 25 cc., 50 cc., 100 c., 150 cc., 200 cc., mud, shallow water, and deep water. Further study justified these divisions, since the first six gave efficient differences in water-content, and the resulting forms all showed differences of structure as well as of growth and form. Seedlings of the same age, and as nearly alike as possible, were transplanted to large pots of which there were four for each of the first six; they were placed in half-barrels for mud and floating forms, and in a barrel for submerged forms. After a few days, when they had become well established, the plants in the pots were watered in the amounts indicated, as often as was necessary to keep the most xerophytic form alive; the soil for the mud form was kept covered with a thin film of water; the leaves of the form in shallow water were kept floating on the surface, and those of the last form submerged just below the surface. The water in which the submerged form grew was aerated by means of a spigot near the bottom of the barrel. From time to time water-content determinations were made of the soil in the pots until it was definitely ascertained that the holard was practically constant. The nine new forms obtained by adaptation showed striking differences in vigor and growth, as may be seen from the figures. In all cases, these were accompanied by distinct and often striking differences in the number and position of the stomata, the amount of sponge and palisade tissues, and the development of air passages. Photographs were made of a typical plant of each form, and the different leaf structures were preserved in permanent mounts. The xerophytic and the submerged form were unable to produce flowers, and it was necessary to develop them anew in each generation. The other forms fruited abundantly, and the succeeding generations of each form were produced from plants which had grown the year before in the same conditions. In addition to the development of a series of new water-content forms, this experiment was begun in the hope of determining whether the modifications of a plastic species tend to become fixed if each new form is grown constantly under the same conditions. A period of four years is too short, however, to throw much light upon this problem.