(Keith Michaels) wrote in message ...
If you slice a beetroot in half you can see obvious growth rings,
even though it grows entirely in one season. What causes the
rings?

The rings are formed by growth originating from secondary cambium
layers, so they form more or less at once, not sequentially.

For the details, see Ernst Artschwager (1926), "Anatomy of the
Vegetative Organs of the Sugar Beet", Journal of Agricultural Research
33(2):143, also online at
http://preserve.nal.usda.gov:8300/ja...43/330143.htm,
esp. starting at page 166.

--
Chris Green