My emitter's snowflakes do not appear in render mode

I moved the snowflake emitter plane to an unused layer, added a new one and added the same particle system as the old one. The new plane works like a charm. I have no idea why, though.

I’m doing a tutorial here: On the snowflake emitter I used a group. Also, the material is more complicated. I still can 't figure out why my snowball emitter object snowballs appear in cycles render but the snowflakes from the snowflake emitter don’t. Can someone tell me what I am doing wrong?

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