How do trees grow? The answer may surprise you. Photosynthesis and respiration produce wood, and all the other parts of a tree. Twigs and roots elongate from growth tissue at the tips, and grow wider from growth tissue under the bark. These special tissues are meristematic tissues. In diameter, a tree will grow TWO rings each year. The lightercolored ring is formed in the spring, followed by a darkercolored ring (usually narrower) grown in the summer. Height growth in most conifers is called “determinate” growth, as a single main leader dominates. Hardwoods (broadleaved trees) don’t have a single main leader. This is called “indeterminant” growth.