Chlorosis is a form of pallor where the chlorophyll grains themselves are fully developed, but their green pigment remains in abeyance owing to a deficiency of iron in the soil, and can often be cured by adding traces of a ferrous salt. The distinction between Icterus, where the organs are only yellow, and Chlorosis proper, where they are nearly white cannot always be maintained. In the typical case only those organs whose cells are still young can become green on adding iron.
Yellowing or False Chlorosis may be experimentally induced by too much carbon-dioxide in the atmosphere. It also often ensues when the roots of plants in the open are waterlogged, owing to the stagnant water not only driving air from the root-hairs but accumulating dissolved substances which poison the plant. Trees frequently thus suffer from "wet feet " when their roots have penetrated down to a sodden impervious subsoil.