Is it true that a magistrate in Ancient Rome automatically became a Senator?

Question

I'm taking a class in Ancient Rome and am a little confused. My text says that "a Roman automatically became a senator when he became a magistrate."

The way I read this passage, if the comitia tributa or concilium plebis selected an aedile (for example), this individual was now automatically serving in the Senate for life? Or, is this individual now eligible to serve in the Senate at some point in the future? I understand cursus honorum, but I did not realize (if I'm reading this correctly) that once selected as a magistrate, he is automatically a senator.

What happened if there were already 300 senators (the maximum) and an aedile who was not previously a senator is selected? Would the senate ranks be automatically expanded to 301 to accommodate this new magistrate?

Please help.

Answer 1

Aediles, praetors, quaestors, and consuls were customarily added to the Senate for life, and were joined by senatores pedarii (non-elected officials in the Senate.) The number of senators, while traditionally 300, varied from time to time as well. In your hypothetical situation, they would likely enroll one less pedarius that year or just expand over 300 until someone died, was removed for corruption, etc. After around 100BC and the Sullan reforms, the senate was vastly expanded to include many more than 300 individuals for the rest of its existence, so from that point, this would be a non-issue.