They are called adventitious roots and are normal and fairly common. They often sprout up all along the stems of tomato plants when the moisture levels are high, especially on those sections of the stem closest to the ground. No problem.

Dave

digdirt beat me to it, so I will just add that adventitious roots are also seen as shallow green, white, or tan bumps on the stem (sticking up perhaps only a millimeter or two).

Sometimes people who haven't seen them before think an insect has pierced the outer skin of the stem and laid eggs in a line along the stem.

The tomato's ability to send out adventitious roots means that if your seven-year-old breaks off a branch, you can cut off the newest several inches of it and root a new plant. And if you don't stake or otherwise support a plant, it will root wherever its stems touch the ground.

Well, Thank you!!