Cambium thin layer of generative tissue lying between

Cambium, thin layer of generative tissue lying between the bark and the wood of a stem, most active in woody plants. The cambium produces new layers of phloem on the outside and of xylem (wood) on the inside, thus increasing the diameter of the stem. In herbaceous plants the cambium is almost inactive; in monocotyledonous plants it is usually absent

There are two types of cambium Cork cambium Vascular cambium

Cork cambium • Cork cambium is a tissue found in many vascular plants as part of the periderm. • The cork cambium is a lateral meristem and is responsible for secondary growth that replaces the epidermis in roots and stems. • It is not found in many herbaceous dicots and some monocots, which usually lack secondary growth.

• The function of cork cambium is to produce the cork, a tough protective material. • Synonyms for cork cambium are bark cambium, pericambium or phellogen. • Phellogen is defined as the meristematic cell layer responsible for the development of the periderm.

• In smaller stems and on typically non woody plants, sometimes a secondary covering form called the periderm. • The periderm forms from the phellogen which serves as a lateral meristem. • The periderm replaces the epidermis, and acts as a protective covering like the epidermis.

The periderm consists of three different layers: • Phelloderm • Phellogen (cork cambium) and • Phellem.

• Cells that grow inwards from the phellogen are termed phelloderm, • Ccells that develop outwards are termed phellem or cork (similar with vascular cambium).

Lenticel • Loosely-packed mass of cells in the bark of a woody plant, visible on the surface of a stem as a raised powdery spot, through which gaseous exchange occurs is the lenticel. • The initial periderm is interrupted at points around the stem by the occurrence of lenticels (Latin lentis, a lentil). These are blister-like, lenticular ruptures in the surface. • The name lenticel comes from the fact that it is lens shaped.

• The cells of the lenticel also tend to expand outside the stem, yielding that blistered appearance. • Each lenticel therefore becomes a pathway through which gases (especially oxygen) can diffuse to the living cells of the bark. • Without sufficient oxygen, cells of bark can die.

Vascular Cambium • The vascular cambium is a lateral meristem in the vascular tissue of plants. • The vascular cambium is the source of both the secondary xylem (inwards, towards the pith) and the secondary phloem (outwards), and is located between these tissues in the stem and root. • A few leaves even have a vascular cambium. • Vascular cambia are found in dicots and gymnosperms but not monocots, which usually lack secondary growth.

The vascular cambium usually consists of two types of cells: • Fusiform initials (tall cells, axially-oriented) • Ray initials (almost isodiametric cells - smaller and round to angular in shape)

• Vascular cambium initials have only primary cell walls that are never lignified. • Their tangential walls are thinner than radial walls and lack primary pit fields. • The radial walls, however, often have numerous orderly arranged primary pit fields that give the walls a "beaded" appearance. • When the cells are dormant they have few and small vacuoles, but in the active state they become highly vacuolated and a central vacuole develops.

• Vascular cambium cells have no intercellular spaces and they grow intrusively. • Cross divisions of fusiform initials may shorten the vertical axis of the cells to shorter cells that can change into ray initials. • The growth of both secondary tissues and rays may be storied (stratified) in which the cells are arranged in uniform horizontal series, or nonstoried (nonstratified) in which such a uniform arrangement does not exist.

Synonyms for cork cambium are bark cambium, pericambium or phellogen. Phellogen is defined as the meristematic cell layer responsible for the development of the periderm. Cells that grow inwards from the phellogen are termed phelloderm, and cells that develops outwards are termed phellem or cork (note similarity with vascular cambium). The periderm thus consists of three different layers:

Structure of the cambium n n Cellular structure of the cambium Size of cambium cells Structure of cambial Cell division in the cambium

Vascular Cambium • The vascular cambium is a lateral meristem in the vascular tissue of plants. • The vascular cambium is the source of both the secondary xylem (inwards, towards the pith) and the secondary phloem (outwards), and is located between these tissues in the stem and root. • A few leaves even have a vascular cambium. • Vascular cambia are found in dicots and gymnosperms but not monocots, which usually lack secondary growth.