As you can see in the first set of pictures, when you are using the shallow round trays to do MicroGreens such as Radish, Broccoli, Cress, Mustard, Field Pea, Wheatgrass etc, it is best to keep the seeds covered for the first few days so that they do not dry out, this clear Perspex cover has holes cut into it to allow for air to flow, but not so much that it will dry out the seeds. It also saves space by allows you to stack them one on top of each other while they are in this germination phase.

When they begin to Sprout, you can un-stack them and still leave the cover on and light will now be able to get through, and then remove the cover once the sprouts begin to lift the lid.