Cambium

a layer of delicate meristematic tissue between the inner bark or phloem and the wood or xylem, which produces new phloem on the outside and new xylem on the inside in stems, roots, etc., originating all secondary growth in plants and forming the annual rings of wood.
Contemporary Examples

What It Takes to Kill a Grizzly Bear Doug Peacock November 22, 2014

Historical Examples

The Nursery Book Liberty Hyde Bailey
The Library of Work and Play: Outdoor Work Mary Rogers Miller
Trees Worth Knowing Julia Ellen Rogers
Trees Worth Knowing Julia Ellen Rogers
Northern Nut Growers Association, Report of the Proceedings at the Third Annual Meeting Northern Nut Growers Association
Encyclopaedia Britannica, 11th Edition, Volume 12, Slice 2 Various
Studies of Trees Jacob Joshua Levison
The Elements of Botany Asa Gray
Proserpina, Volume 2 John Ruskin

noun (pl) -biums, -bia (-bɪə)
(botany) a meristem that increases the girth of stems and roots by producing additional xylem and phloem See also cork cambium
n.
cambium
(kām’bē-əm)
Plural cambiums or cambia
A cylindrical layer of tissue in the stems and roots of many seed-bearing plants, consisting of cells that divide rapidly to form new layers of tissue. Cambium is a kind of meristem and is most active in woody plants, where it lies between the bark and wood of the stem. It is usually missing from monocotyledons, such as the grasses. ◇ The vascular cambium forms tissues that carry water and nutrients throughout the plant. On its outer surface, the vascular cambium forms new layers of phloem, and on its inner surface, new layers of xylem. The growth of these new tissues causes the diameter of the stem to increase. ◇ The cork cambium creates cells that eventually become bark on the outside and cells that add to the cortex on the inside. In woody plants, the cork cambium is part of the periderm. See also secondary growth.
cambium [(kam-bee-uhm)]