Pollen from a variety of common plants: sunflower, morning glory, hollyhock, lily, primrose and caster bean. The largest one at center is nearly 100 microns wide (human hair is approximately 100 microns thick). (Dartmouth Electron Microscope Facility ~ Dartmouth College)
Now I know why honey bees are so fond of pollen---because it is so beautiful!
Please visit The Big Picture for a fascinating 32-photo essay entitled Peering into the Micro World.