Mains power is a constant-voltage system. As such, everything is wired in parallel.
Constant-current power is not unheard-of in mains wiring, however it is notoriously dangerous and as such, is used in extreme specialty applications and requires special handling - e.g. shorting the output of CC transformers to keep them from trying to create infinite voltage. Transformers don't have crowbar/limiting circuits like electronic supplies do.
Series would be a really weird thing to do, and you would need precautions against a device malfunctioning, or worse, the next occupant doing something dangerously moronic because he didn't understand your setup -- the latter reason is why "weird setups that require knowledge to use safely" are prohibited.