Use Modifier Stack

– If checked this options tells blender to evaluate the modifiers in the order they appear in the modifier list.

– In this example an array modifier was applied (before the particle system) to duplicate a sphere (the emitter).

– Here you can see the array modifier:

Blender Hair Stack

– The 500 hairs are distribued among the two spheres when this option is checked:

Blender Hair Use Modifier Stack