Trees can develop interesting features, given their growing conditions and environment. Usually, a tree will grow having the different bands creating “rings” throughout the growth of the tree. The two bands look different because the small cells created by the tree in the Summer absorb more light and there for look darker. You can see in the photos the dark bands have much smaller cells, creating a definite “ring”. We know that it takes a season or “year” to create the band, thus why you can count a tree’s age, by counting the rings.
Some tree rings are wide and some are narrow. Wide rings form during a year when the weather was very good for growth, such as warm and wet. Narrow rings form during drier years and cooler years.
The picture on the left shows the center of the ring or “pith” to be in the center of the stump, while the picture on the right shows the center ring to be on the right. What causes this feature? Well, as Markus explained that trees that are grown on the side of a hill will compensate by growing the rings toward the side that needs the support of the tree to grow straight on the side of the mountain. This is why the center of the tree is pushed toward the right, the side that would be directly on the hillside.