Stem circumference, xylem pressure potential (P), and leaf surface resistance were measured in a dominant forest-grown white oak (Quercus albaL.) tree from the beginning of, through the development of, and to recovery from a major drought in mid-Missouri. Continuous recording of several environmental variables and periodic measurements of soil moisture were made in coordination with the above plant variables. As baseP(Pmeasured just before sunrise) and soil moisture decreased, net day-to-day and even week-to-week stem shrinkage was observed. Periodic thunderstorms alleviated soil and plant water deficits and stem circumference recovered. Excellent relationships were noted between soil moisture in the upper 30 cm of a 107-cm profile and either basePor stem circumference.Four clear and 2 cloudy days with rain are presented to illustrate diurnal patterns in the aforementioned variables. The generalized pattern of diurnal fluctuations in stem circumference consisted of early morning shrinkage, which continued to a 1500- to 1700-h. (true solar time) minimum, and subsequent recovery. Hysteresis loops resulted when stem circumference was plotted againstP. Maximum diurnal fluctuations in stem circumference were greatest when soil moisture had been depleted slightly below field capacity. Further depletion led to lower values ofP, stomatal closure, restricted plant water loss, and reduced stem shrinkage. The relationship between flux (vapor pressure deficit – leaf surface resistance) andPis also described and it provided a possible means of modelingPin plants. The possible role of the stem reservoir in augmenting foliar water deficits is presented and discussed.