Particles not appearing on mesh when I apply


I’m trying to set up a cloud rig (following a tutorial), but when I attach the cloud mesh to the particle, instead of the cloud becoming full of particles, nothing happens. Here is an example of what I mean. The top is my attempt (no particles on the cloud mesh), the bottom (the tutorial) has lots particles on the mesh Imgur: The magic of the Internet

Any ideas what this might be? I have googled this issue and some people have suggested it may be Auto-Activate being off, but I’ve checked that for the both cloud and particle objects, and for both it’s set to auto-activate.