Wood, like all plant material, consists of cells. “Woody” plants are able to attain a large size because of a complex substance know as ‘lignin’, that binds the various cells together. Wood is classified as ‘hardwood’ if it has vessels in its structure, or ‘softwood’ if it does not. Softwoods have a more fibrous structure. The term hardwood does not relate to the hardness of the wood, but is the common word for plants of the dicotyledon sub-group. Hardwoods are often more dense and more difficult to work than softwoods, but there are many exceptions to this. The major chemical components of wood are cellulose, hemicelluloses and lignin. There are also a number of minor components known as extractives, which vary depending on the species.