<JP>
根から葉裏に分布する気孔まで続く一連の木部（導管）を流れる樹液の流れを樹液流（Sap FLow）と呼びます．導管のサイズと茎/幹/枝断面積内での分布様式は植物によって様々です．樹体内を流れる樹液流は蒸散が駆動力であり、大気飽差と日射によって変わる気孔開度によってその流量は変化します．
気孔開度は水道でいうところの蛇口の開き具合に相当し、葉が受ける受光量や風速、湿度によって変化します．大気飽差は水流を生む水圧（実際は水道とは逆で乾燥した大気が葉から水を引っ張る負の力）に相当します．
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<EN>
The sap flow that flows through a series of xylems conduit that extends from the roots to the stomata distributed on the back of the leaves is called sap flow. The size of the conduit and its distribution within the stem / stem / branch cross-sectional area vary from plant to plant. The sap flow in the tree body is driven by transpiration, and its flow rate changes depending on the atmospheric opening and the stomatal opening that changes due to solar radiation.
The stomatal aperture is equivalent to the opening of a water tap, and it varies depending on the amount of light received by the leaf, wind speed and humidity. Vapor pressure deficit corresponds to the driving force that produces water flow (the negative force of the dry air pulling water from the leaves).
