Pressure bomb

A pressure bomb or pressure chamber or Scholander bomb is an instrument with which it is possible to measure the approximate water potential of plant tissues. A leaf attached to a stem is placed inside a sealed chamber and pressurized gas is added to the chamber slowly. As the pressure increases at some point sap will be forced out of the xylem and will be visible at the cut end of the stem. The pressure that is required to do so is equal and opposite to the water potential of the leaf. Pressure bombs are very durable and mechanically simple, which make them a popular alternative to traditional methods for taking field measurements.