Note the very narrow ring in 1977 reflecting a dry year. Reaction wood forms when a tree tilts. There are many elements that may cause a tree to tilt, like wind and snow. The sample also shows a branch growing from the center of the tree outward. Comparing the two samples, which are about the same size around, we see that growth conditions were more favorable for the white fir than for the Douglas-fir, because of the wider rings.
Growth is from the left to right.
Earlywood is marked by lighter colored cells, while latewood is marked by the dark bands. Together, they make up one annual tree ring. Note the subtle false rings in the fourth ring from the left and in the fifth ring from the right. These two examples are not so obvious, but sometimes in certain tree species growing in certain environments, false rings can look just like true rings. Without training in crossdating, false rings can be problematic when attempting to crossdate tree ring patterns.