Particular: Where did Aux Systems go?

Older versions of Particular had something called Aux Systems, which were particles that emitted from other particles. This exact same effect has been incorporated into the emitter section of any secondary particle systems under Emitter Type > Emit from Parent System.

Once this option is selected, you can choose which parent you want the emitter to come from, allowing you to attach secondary systems to the primary, or even other secondary systems, giving you more freedom of how these particle interact with one another.​