Encyclopedia of toxicology, second edition. Wexler P, Anderson BD, De Peyster A, Gad SC, eds. San Diego, CA: Academic Press, 2005 Mar; :464-467
Tree species are classified either as gymnosperms, which generally have needle-like leaves, or as angiosperms, which generally have broad leaves and are deciduous in temperate climates. In practice, trees usually are classified as softwoods, hardwoods, or tropical woods. Softwoods include the temperate gymnosperms or conifers; hardwoods include the temperate angiosperms; and tropical hardwoods primarily are angiosperms, but also include some gymnosperms that thrive in tropical climates. Wood is composed primarily of cellulose, hemicellulose, and lignin. In addition to these basic components, wood also contains many organic compounds, known as "wood extractives". Wood extractives serve to protect trees from bacteria, fungi, and other potentially harmful agents. They also provide grain and color to the wood. These extractives typically make up 5-30% of the wood mass. Softwoods and hardwoods differ in cellular structure as well as chemical composition and there is great variability between species. Biologically active chemicals found in wood include terpenes, lignans, stilbenes, tannins, flavinoids, and quinines.
Wood; Wood-dusts; Woodworkers; Woodworking; Plants; Plant-dusts; Plant-substances; Plant-cells; Woodworking-industry; Furniture-industry; Furniture-manufacture; Furniture-workers; Biological-agents; Logging-workers; Lumber-industry; Lumber-industry-workers; Pulp-industry; Construction; Construction-materials; Construction-workers; Dust-exposure; Dusts