為探討在極端乾旱情形下，柑桔果實與葉片之間水份之互動關係，本試驗以帶有果實與葉片之葡萄柚枝條為材料，模擬在極端乾旱缺水之情況下，觀察果實大小及葉片、果實蒸散作用之變化，並測定葉片、果皮、果肉之水份潛勢。另以放射性水注射進入果梗後追蹤水份在葉片、枝條、果皮、果肉間之流向與流量，以瞭解果實蒸散作用與木質部水份回流對果實水份含量及水份潛勢之影響。結果顯示：果實蒸散作用與木質部水份回流在果實中可同時發生，在帶有果實之枝條上，果實與葉片之蒸散作用均較旺盛，果實剪下後，果實與葉片之蒸散作用均減緩。果實經由蒸散作用喪失之水份與經由木質部水份回流喪失之水份相近，分別為果實原來含水量之2.1%與2.2%。剛剛進入砂囊（Juice Sacs）之水份會先被木質部回流之水流倒抽而離開果實。中果皮與果肉組織之水份均可能經由木質部回流至葉片，但回流之水量果皮部份在4天之試驗期間佔其原含水量之5.4%，果肉部分則僅佔1%。因木質部水份回流而造成之水份潛勢降低，在中果皮部分約為0.6MPa，果肉組織則為0.1MPa。果實蒸散作用喪失之水份主要係來自中果皮，而非來自果肉組織。
Detached fruit-bearing branches (1 fruit and ca 5 leaves each) were harvested from 10-year-old grapefruit trees to quantify the extent to which xylem back-flow can remove water from fruit to leaves, and the amount of water arising from different sources in fruit. Tritiated water was used to trace the movement from fruit to leaves and, together with total water, to quantify th efflux from fruit.The results showed that both fruit transpiration and water exit via xylem back-flow were found to occur within a given 24-hour period. Both leaves and fruit transpired more water when on fruited branches, than when fruit were severed. Total water losses from fruit via xylem back-flow and fruit transpiration were similar (2.1% vs 2.2% of original tissue water). A comparison between exit of total and tritiated water indicated that newly arrived water in juice sacs was the first to leave. Albedo and possibly juice sacs both contributed to the water efflux from fruit via xylem back-flow, although peel lost a mean of 5.4% of its tissue water in 4 days. vs 1.0% from juice sacs during the same period. Concomitant decreases in water potential were ca 0.6 MPa in albedo and ca 0.1 MPa in juice sacs due to effects of xylem back-flow. Transpirational water loss from fruit appeared to arise from albedo rather than from juice sacs during this experimental period.
