The cambium has been variously defined as follows: "The actively dividing layer of cells that lies between, and gives rise to, secondary xylem and phloem (vascular cambium)" (IAWA 1964); "A meristem with products of periclinal divisions commonly contributed in two directions and arranged in radial files. Term pre­ ferably applied only to the two lateral meristems, the vascular cambium and cork cambium, or phellogen" (Esau 1977); and, "Lateral meristem in vascular plants which produces secondary xylem, secondary phloem, and parenchyma, usually in radial rows; it consists of one layer of initials and their undifferentiated deriva­ tives" (Little and Jones 1980). Clearly, the cambium is a diverse and extensive meristem, and no one defini­ tion will encompass all manifestations of what anatomists consider cambium. Its diversity and extent are further exemplified by a single plant, such as a temperate­ zone tree, in which procambium is initiated in the embryo and perpetuated throughout every lateral, primary meristem before giving rise to cambium in the secondary body. The cambium thereafter performs its meristematic task of producing daughter cells that differentiate to specialized tissue systems. The cam­ bium, however, does not remain static. Its derivatives vary either in form, or TImc­ tion, or rate of production at different positions on the tree, with age of the tree, and with season of the year. Moreover, the cambium responds both to internal sig­ nals and to external stimuli such as environment or wounding.

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1 Introduction.- 2 Fossil Evidence.- 3 Historical.- 3.1 Derivation of the Word Cambium.- 3.2 The Concept of Cambium as a Tissue.- 3.2.1 The Role of Cell Division.- 3.2.2 The Role of Cell Protoplasm.- 4 Defining the Cambium.- 4.1Cambial Cell Theories.- 4.1.1 "Siamese Twin" Theory of Hartig.- 4.1.2 Uniseriate Initial Theory of Sanio.- 4.1.3 Multiseriate Theory of Raatz.- 4.1.4 Uniseriate vs. Multiseriate Theories.- 4.2 Special Criteria.- 4.2.1 Sanio's Rules.- 4.2.2 Additional Rules.- 4.2.3 Role of Mother Cells.- 4.2.4 Tangential Cell Alignment.- 4.3 Reconciliation.- 4.4 Terminology.- 4.5 Special Features.- 4.5.1 Sanio's Four.- 4.5.1.1 Xylem.- 4.5.1.2 Phloem.- 4.5.2 Bars of Sanio - Trabeculae.- 4.5.3 Rims of Sanio - Crassulae.- 4.5.4 Bars vs. Rims of Sanio.- 4.5.5 Monogene vs. Polygene Cambia.- 4.5.6 Cambial vs. Apical Initials.- 5 Cambial Cell Characteristics.- 5.1 Cell Shape.- 5.1.1 Effect of Cell Shape on Division.- 5.2 Fusiform Initial Size.- 5.2.1 Fusiform Initial Volume.- 5.3 Ultrastructure.- 5.3.1 Nucleus.- 5.3.1.1 Fusiform Initials.- 5.3.1.2 Ray Cell Initials.- 5.3.1.3 Nuclear Migration.- 5.3.1.4 DNA Content.- 5.3.1.5 Nucleoli.- 5.3.2 The Vacuole.- 5.3.2.1 Protoplasmic Streaming.- 5.3.3 Organelles.- 5.3.3.1 Gymnosperms.- 5.3.3.2 Dicotyledons.- 5.4 Cytochemistry.- 5.4.1 Starch.- 5.4.1.1 Gymnosperms.- 5.4.1.2 Dicotyledons.- 5.4.2 Lipids.- 5.4.3 Proteins.- 5.4.4 Phytoferritin.- 5.4.5 Tannins.- 5.4.6 Chlorophyll.- 5.4.7 Miscellaneous Constituents.- 5.5 Cambial Cell Division.- 5.5.1 Mitotic Index.- 5.5.2 Cambial Cell Cycle.- 5.6 Cambial Aging.- 6 Anticlinal Cambial Divisions.- 6.1 Pseudotransverse and Transverse Divisions.- 6.1.1 Occurrence.- 6.1.1.1 Analysis.- 6.1.2 Cell Length at Division.- 6.1.3 Cell Wall Orientation.- 6.1.4 Length of Cell Plate.- 6.1.5 Cell Elongation.- 6.1.5.1 Proximal End Growth.- 6.1.5.2 Distal End Growth.- 6.1.5.3 Sister Cell Polarity.- 6.2 Radial Anticlinal Divisions.- 6.2.1 Storied Cambia.- 6.2.1.1 Storied Rays.- 6.3 Fates of Initial Cells.- 6.3.1 Survival of Initial Cells.- 6.3.1.1 Fusiform Cell Length.- 6.3.1.2 Ray Contacts.- 6.3.2 Failure of Initial Cells.- 6.3.2.1 Cell Elimination.- 6.3.2.2 Segmentation to Parenchyma.- 6.3.2.3 Segmentation to Rays.- 6.2.3.4 Complete Segmentation.- 6.2.3.5 Partial Segmentation.- 6.4 Tangential Increase of Cambium.- 6.4.1 Nonstoried Cambia.- 6.4.1.1 Fusiform Initials.- 6.4.1.2 Ray Cell Initials.- 6.4.2 Storied Cambia.- 6.5 Frequency of Anticlinal Divisions.- 6.5.1 Age of Tree.- 6.5.2 Rate of Growth.- 6.5.2.1 Eccentric Stems and Branches.- 6.5.3 Location Within the Growth Ring.- 6.5.4 Position in the Tree.- 6.5.4.1 Height in the Stem.- 6.5.4.2 Branches.- 6.5.4.3 Branch Crotches.- 6.5.4.4 Roots.- 6.5.4.5 Living Stumps.- 6.5.5 Variations Among Species.- 6.5.6 Biennial Frequency.- 6.6 Aberrant Anticlinal Divisions.- 6.6.1 Localized Domains.- 6.6.2 Migrating Domains.- 6.6.2.1 Wavy Grain.- 6.6.2.2 Interlocked Grain.- 6.6.2.3 Spiral Grain.- 6.6.2.4 Whirled Grain.- 6.6.2.5 Circular Vessels and Tracheids.- 6.6.3 Wave Pattern of Domains.- 6.6.4 Theoretical Interpretations.- 6.7 Mechanism of Cell Elongation.- 6.7.1 Sliding Growth.- 6.7.2 Symplastic Growth.- 6.7.3 Intrusive and Interpositional Growth.- 6.7.4 Objections to Intrusive Growth.- 6.7.4.1 Intrusive Tip Growth.- 6.7.4.2 Primary Pit Fields.- 6.7.4.3 Plasmodesmata.- 6.7.5 Forked Cells.- 6.7.6 Reconciliation.- 7 Periclinal Cambial Divisions.- 7.1 Nonstoried Cambia.- 7.1.1 Intracambial vs. Extracambial.- 7.1.2 Gymnosperm Xylem.- 7.1.2.1 Tracheids.- 7.1.3 Dicotyledon Xylem.- 7.1.3.1 Vessels.- 7.1.3.2 Vesselless Dicotyledons.- 7.1.3.3 Libriform Fibers.- 7.1.3.4 Living Wood Fibers.- 7.1.3.5 Axial Parenchyma.- 7.1.4 Dicotyledon Phloem.- 7.1.4.1 Sieve Elements.- 7.1.4.2 Phloem Fibers.- 7.2 Storied Cambia.- 7.3 Anomalous Cambia.- 8 Rays.- 8.1 Medullary Rays - Historical.- 8.2 Classification of Rays.- 8.2.1 Primary Rays.- 8.2.2 Secondary Rays.- 8.3 Ray Dynamics.- 8.3.1 Secondary Ray Origin.- 8.3.1.1 Ray Spacing.- 8.3.1.2 Ray Cell Initials.- 8.3.2 Ray Numbers.- 8.3.3 Division of Ray Cell Initials.- 8.3.4 Ray Mergers.- 8.3.4.1 Gymnosperms.- 8.3.4.2 Dicotyledons.- 8.3.5 Loss of Ray Cell Initials.- 8.3.6 Ray Splitting.- 8.3.6.1 Intrusion of Fusiform Initials.- 8.3.6.2 Reversion of Ray Cell Initials.- 8.3.7 Discontinuous Rays.- 8.3.8 Ray Failure.- 8.3.9 Ray Widths.- 8.3.10 Ray Cell Size.- 8.3.11 Ray Volume.- 8.4 Selected Examples.- 8.4.1 Gymnosperms.- 8.4.1.1 Primary Rays.- 8.4.1.2 Secondary Rays.- 8.4.1.3 Fusiform Rays.- 8.4.1.4 Haselwuchs.- 8.1.4.5 Pseudorays.- 8.4.2 Dicotyledons.- 8.4.2.1 Primary Rays.- 8.4.2.2 Secondary Rays.- 8.4.2.3 Rayless Woods.- 8.5 Radial Plates and Erect Cells.- 8.6 Effect of Eccentricity.- 8.7 Miscellaneous Features.- 9 Intercellular Spaces.- 9.1 Nonsecretory.- 9.2 Secretory.- 9.2.1 Dicotyledons.- 9.2.1.1 Traumatic Canals.- 9.2.2 Gymnosperms.- 9.2.2.1 Primary Resin Canals.- 9.2.2.2 Secondary Resin Canals - Axial.- 9.2.2.3 Secondary Resin Canals - Radial.- 9.2.2.4 Axial-Radial Canal Anastomoses.- 9.2.2.5 Traumatic Resin Canals.- 9.2.2.6 Resin Cysts and Pockets.- 10 Cambial Wounding.- 10.1 Introduction.- 10.2 Barrier Zone.- 10.3 Mechanical Wounds.- 10.3.1 Shallow Wounds.- 10.3.1.1 Exposed Surfaces.- 10.3.1.2 Enclosed Surfaces.- 10.3.2 Deep Wounds.- 10.3.2.1 Radial Cracks and Fissures.- 10.3.3 Bark Strips.- 10.3.4 Split Stems.- 10.3.5 Girdling.- 10.3.5.1 Phloem Bridges.- 10.3.5.2 Spiral Girdles.- 10.3.6 Grafting.- 10.3.6.1 Graft Inversions.- 10.3.6.2 Natural Root Grafts.- 10.3.6.3 Natural Stem Grafts.- 10.3.7 Pruning Wounds.- 10.3.8 Decapitation.- 10.3.8.1 Cladoptosis.- 10.4 Ionizing Radiation.- 10.5 Biological Wounds.- 10.5.1 Tumorous Growths.- 10.5.2 Insects.- 10.5.2.1 Scales.- 10.5.2.2 Aphids.- 10.5.2.3 Bark Beetles.- 10.2.5.4 Cambial Miners.- 10.5.3 Nematodes.- 10.5.4 Birds.- 10.5.5 Mammals.- 10.5.6 Parasitic Plants.- 10.5.6.1 Exocarpus bidwillii.- 10.5.6.2 Mistletoes.- 10.6 Environmental Factors.- 10.6.1 Frost.- 10.6.2 Drought.- 10.6.3 Flooding.- 10.6.4 Lightning.- 10.7 Cambial Marking.- 10.7.1 Pinning Method.- 10.7.2 Electrical Stimulation.- 10.8 Cambial Electrical Resistance.- 10.9 Reconciliation.- 11 Cambial Zone Characteristics.- 11.1 Cambial Zonation.- 11.2 Radial Cell Wall Thickness.- 11.3 Number of Cambial Zone Cells.- 11.3.1 Dormant Cambium.- 11.3.2 Active Cambium.- 11.4 Cambial Reactivation.- 11.4.1 Bark Slippage and Cambial Swelling.- 11.4.2 Xylem vs. Phloem Reactivation.- 11.5 Alterna…