1 Introduction.- 1.1 Prehistoric and Ancient Use.- 1.2 Changing Uses of Forests.- 2 Definitions and Descriptions.- 2.1 Introduction.- 2.2 Sapwood.- 2.2.1 Definitions.- 2.2.1.1 Sapwood.- 2.2.1.2 Included Sapwood.- 2.2.2 Area of Sapwood in Log Cross-Sections.- 2.2.3 Variation of Area of Sapwood.- 2.2.3.1 In a Species.- 2.2.3.2 In Different Species.- 2.2.3.3 Due to Age of Tree.- 2.2.3.4 Due to Rate of Growth.- 2.2.3.5 Due to Environment.- 2.2.4 Sapwood Contents.- 2.2.5 Discolored Sapwood.- 2.3 Intermediate Wood.- 2.3.1 Description.- 2.3.2 Occurrence.- 2.4 Transition Zone.- 2.4.1 Definition.- 2.4.2 Description.- 2.4.3 Occurrence.- 2.4.3.1 Heartwood Boundary Stain.- 2.5 Heartwood.- 2.5.1 Definition.- 2.5.2 Description.- 2.5.2.1 Appearance.- 2.5.2.2 Level of Maximum Area.- 2.5.2.3 Regular Heartwoods.- 2.5.2.4 Irregular Heartwoods.- 2.5.2.5 Variations in Appearance.- 2.6 Tree Exudates and Extracellular Materials.- 2.6.1 Definitions.- 2.6.1.1 Intercellular Secretory Spaces, Cavities, and Shakes.- 2.6.1.2 Intercellular Canals.- 2.6.1.3 Pitch Tubules and Stones.- 2.6.1.4 Pockets, Veins, and Streaks.- 2.6.2 Types of Exudate or Deposit.- 2.6.2.1 Resin.- 2.6.2.2 Gum.- 2.6.2.3 Kino.- 2.6.2.4 Latex.- 2.6.2.5 Manna.- 2.6.2.6 Amber.- 2.6.2.7 Balsam.- 2.6.2.8 Maple Sugar.- 2.6.2.9 Crystalline Compounds.- 2.6.3 Rate of Formation.- 3 Historical Aspects.- 3.1 The Use of Durable Woods.- 3.2 Exudates.- 3.3 Varnishes and Lacquers.- 3.4 Gums.- 3.5 Tannins.- 3.6 Dyes.- 3.7 Perfumes.- 3.8 Rubber.- 3.9 Medicines.- 3.10 Lessons from History.- 4 Influence of Forestry Aspects.- 4.1 Variation of Heartwood Volume.- 4.1.1 Heritability.- 4.1.2 Effect of Growth Rate and Crown Size.- 4.1.3 Influence of Environment.- 4.1.4 Influence of Injury and Health.- 4.2 Formation of Exudates.- 4.2.1 From Bark and Wood.- 4.2.2 From Wood.- 4.2.3 Addition of Stimulants.- 5 Chemical Features.- 5.1 Water and Gases.- 5.2 Inorganic Compounds.- 5.3 Storage Substances and Intermediates.- 5.4 Nitrogenous Compounds.- 5.5 Ethylene.- 5.6 Type of Extractives.- 5.6.1 Galactans and Cyclitols.- 5.6.2 Terpenoids.- 5.6.3 Fatty Acids and Related Compounds.- 5.6.4 Phenolic Compounds.- 5.6.4.1 Simple Phenols and Phenolic Acids.- 5.6.4.2 Lignans.- 5.6.4.3 Stilbenoids.- 5.6.4.4 Flavonoids.- 5.6.4.5 Quinones.- 5.6.4.6 Polymerized Polyphenols.- 5.6.4.7 In Different Tissues.- 5.7 Amount of Extractives.- 5.7.1 Position of Sample in the Tree.- 5.7.2 Effects of Rate of Growth 1ll.- 5.7.3 Effect of Site.- 5.7.4 Genetic Differences.- 5.7.5 Crystals.- 5.8 Reagents for Heartwood Detection.- 5.9 Exudates.- 5.9.1 Resin.- 5.9.2 Gum.- 5.9.3 Kino.- 5.9.4 Latex.- 5.9.5 Manna.- 6 Biological Features.- 6.1 Sapwood.- 6.1.1 Wood Tissues.- 6.1.2 Lumen Volume.- 6.1.3 Deposition of Extractives on Wall Surfaces.- 6.1.4 Impregnation of Cell Walls.- 6.1.5 Parenchyma.- 6.1.5.1 Volume.- 6.1.5.2 Cell Wall.- 6.1.5.3 Cytology.- 6.1.6 Respiration and Enzymes Activity.- 6.2 Transition Zone.- 6.2.1 Seasonal Variations.- 6.2.2 Appearance.- 6.2.3 Water Content.- 6.2.4 Pit Aspiration and Tylosis Formation.- 6.2.5 Cytology of Parenchyma Cells.- 6.2.6 Respiration.- 6.2.7 Enzyme Activity.- 6.2.8 Formation of Extractives.- 6.3 Heartwood.- 6.3.1 Seasonal Formation.- 6.3.2 Appearance.- 6.3.3 Respiration and Enzyme Activity.- 6.3.4 Location of Extractives.- 6.4 Wound Wood and Chemically Affected Wood.- 6.4.1 Wound Wood.- 6.4.2 Paraquat-Treated Woods.- 6.4.2.1 Biochemical Changes Due to Paraquat.- 6.4.3 Ethylene-Treated Wood.- 6.4.4 Knots.- 6.5 Exudates.- 6.5.1 General.- 6.5.2 Resin Formation.- 6.5.2.1 Anatomy of Pockets.- 6.5.3 Gum Formation.- 6.5.4 Kino Formation.- 6.5.4.1 Anatomy of Veins and Pockets.- 6.5.4.2 Chemistry of Kino Formation.- 6.5.5 Rubber Tapping.- 7 Function, Formation, and Control of Heartwood and Extractives.- 7.1 Function and Volume of Sapwood.- 7.1.1 Function.- 7.1.2 Volume.- 7.2 Types and Formation of Heartwood.- 7.2.1 Introduction.- 7.2.2 Types of Heartwood.- 7.2.2.1 Regular Heartwoods.- 7.2.2.2 Other Types.- 7.2.3 Conclusions.- 7.3 Features of Heartwood and Woundwood.- 7.3.1 Some Theories of Heartwood Formation.- 7.3.1.1 Natural Causes.- 7.3.1.2 Accumulation of Gas and Control of Water Content.- 7.3.1.3 Initiation by Fungi and Hormones.- 7.3.2 Anatomical Changes.- 7.3.3 Occurrence of Extractives.- 7.4 The Transition Zone and its Formation.- 7.5 Function of Extractives and Exudates.- 7.6 Formation of Exudates and Extractives.- 7.6.1 Differences in Composition.- 7.6.2 Site of Formation.- 7.6.2.1 Exudates.- 7.6.2.2 Extractives.- 7.6.3 Amounts.- 7.6.4 Type of Extractives in Tissues.- 7.7 Initiation of Formation of Heartwood, Extractives, and Exudates.- 7.7.1 Initiation by Displacement of Water.- 7.7.2 Initiation by Changes in Ethylene Levels and in Hormonal Balance.- 7.8 Factors Controlling the Nature of Extractives and Exudates.- 7.9 Activities at Cellular Levels.- 7.10 Conclusions.- References.