Wood is the hard fibrous material that forms the main substance of the trunk or branches of a tree or shrub. Wood has been extremely important for human culture as both a fuel and building material. Even in a world of new technological advances, wood remains very important. The reason for this is because of the cheap and effect ways it can be used. As a building material, it be easily shaped for making used for making boats for transportation, shelters, and even simple utensils. Wood has amazing physical properties and is amazingly designed. There are numerous layers that build the tree in the strongest way possible and keep it standing even up to hundreds of feet.
Wood is a a heterogeneous substance. It is composed of cells with cell walls that are composed of cellulose and hemicellulose. Cellulose is the most common polymer on the planet. It is fiber (polymer) made of glucose molecules, and it is used as a support structure for the cell walls. There are two main types of wood: hardwoods and softwoods. Most hardwoods are angiosperms (seed shell) and have two types of vertically running cells. These are used as a sort of pipes to run sap through them. The way they are given their strength is by their thick cell walls. These walls are made of cells called rays. These act as the storage. The main hardwoods.  Soft woods are gymnosperms (no seed shell).They have more one of a kind cells and because of this the structure is more well put together than of hardwoods. This means that there are no visible pores as there are in hard woods. Most of the woody tissue is made up of long narrow cells called tracheids, which passes the sap through the tree. Softwood, like hardwoods, also have ray cells in them which strengthens the bark. As in every tree and plant they use cellulose as a support system in their cell walls. 
Wood is one of the most common materials on earth. It comes from trees and woody plants which are in abundance in productive ecosystems. There are so many uses for wood that it would be hard to live without it. Wood has two main uses: fuel and construction. Wood was mostly used as fuel for thousands of years until it was replaced with gas stoves and heaters. It is still used in rural areas and more underdeveloped countries around the world.  As a construction material, wood is used to build houses, boats, shelters etc. Houses have been built out of wood since the very beginning of house making. It is still one of the main construction materials used to build houses and probably always will be. There are many different types of wood used in construction however. It is mainly picked by the region the building is being done and the weather of the area. Even houses that are not made of wood will still have a wood frame to keep the house together. Boats have been always built out of wood and never really anything else until the 19th century. Only on occasion are wood boats still made. Elm is the most popular of woods for boats because of its resistance to rot. 
There are many different properties in wood. There are knots, colors, growth rings, etc. A knot is known as a certain imperfection in the wood, which makes it weaker, it also gives the wood a certain type of individuality. A knot is a portion of a branch inside of the tree or a certain large branch. This usually ends up being in a sort of cone shape with a little pointed tip. The knot could also be a dormant bud inside of the wood. These knots can strengthen or weaken the wood depending on where it is located. The knots weakening effect can be a very serious thing in the lumber industry and often is the reason why certain lumber is rejected. Knots do not give the wood a flexible feature but the certain fibers in the grain of the wood. Growth rings are a vital part of the life of a tree. They can show whether or not there was a drought, local fire, flood, injuries, or even if diseases had occurred. These rings are formed each year with the growth of new cells which end up being called annual growth rings. The growing season starts in the spring and starts the circle with a light colored wood and ending with a dark colored wood at the end of the season. Over time most of the wood dies and you are left with darkening rings. If you want to tell the age of a tree you count the rings starting in the middle and working your way out.
The chemical composition of a tree is not determined by an individual tree but determined by many. The reason for this is because the substances in them are always varying depending on the area, climate, and happenings that occur in the area. To find all of the data used in finding this data took a lot of research and a lot of time. The reason for this is because all of the trees had to be examined and experimented on in all regions and areas. They also had to test all of the different types of trees.  The chemical composition of wood is not always the same but is usually at 50% carbon, 6% hydrogen, 1% other, 42% oxygen, 1% nitrogen. Wood also contains many other compounds in an extremely small number. The difference between a hardwood and a softwood is its lignin. The lignin in a certain type of wood varies and the density of it determines its characteristic. The four main components in wood are water, cellulose, hemicellulose and lignin. The cellulose consists of about 42%. The hemicellulose varies anywhere from 20-30% depending on the type of tree it also varies depending on the amount of cellulose in the tree. The forth component is lignin. The lignin controls the amount of water in the wood and gives it strength. All of these combined will form the structure and strength of the tree. 
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