Questions and Answers about BIOLOGY

by Ken Miller and Joe Levine


QUESTION: How can you tell how old the root of a plant is? (Caito, from California)

Let's start with the obvious: if the plant is an annual, its roots are going to be less than a year old (since annuals only live through one growing season). Also, even on a perennial plant that is many years of age, new roots and root hairs are produced all of the time. Therefore, not all roots are indicative of a plant's age.

However, in most woody plants, new wood is added to existing roots in a pattern that varies with the growing season. In the summer growing season, the cells are large and have thin walls, which makes the wood appear light in color. In the winter, the cells are smaller with thick walls, and the wood appears darker. This produces a pattern of annual rings, as described on pages 592-593 of the Dragonfly book.

The important point here is that woody roots display the same pattern of annual rings as do the stems or trunk of a woody plant or tree. Properly interpreted, they allow one to estimate the age of the root.

For more information on how annual rings allow the age of a woody plant to be determined, visit the Laboratory of Tree Ring Research at the University of Arizona:


Ken Miller (6/12/02)

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(A web site developed by Ken Miller and Joe Levine to provide scientific and educational support for teachers and students using our textbooks)