Note the Thick-walled cells in this wood sample. The cells with large diameters are Pores. The smaller cells are mostly Fibers . Hard Woods like koa contain a high proportion of Fibers . The red color signifies the presence of Lignin.
Wood is composed of many concentric circles of xylem.
These are deposited as long as the plant stays alive. They accumulate over time because they contain thick-walled, cells which are lignified. The stem below shows many growth rings in its wood. Start at the center and proceed towards the outside.