Potometer. A potometer can be used to measure the rate of transpiration that's proportional to water uptake. Transpiration cannot be measured directly as some of the water will be used in photosynthesis.

How do you measure water loss in a plant?

A potometer measures water loss from leaves. A bubble potometer measures the rate of water loss from a plant by transpiration. A weight photometer measures the amount of water lost by a plant through transpiration. The washing line method is used to prove that most water loss occurs from the lower surface of the leaf.

What unit is transpiration measured in?

In SI notation transpiration may be expressed as milligrams H2O per meter squared per second (mg'nr^s"1). For example, a transpiration rate of 5 ^g«cm"'«s"1 would, in SI units, be expressed as 0.5 mg'irr^s"1. Water Relations.