What is this picture?

Question

What is shown in this image?

Accepted Answer

onion skin cells (macro). # Onion Skin Cells: Nature's Perfect Microscope Slide

Onion skin cells are so transparent and perfectly arranged that they were literally the first cells ever observed under a microscope back in the 1600s—making them responsible for kickstarting the entire field of cell biology. Even cooler, their cell walls are so rigid and their arrangement so orderly that they remain one of the best teaching tools in biology classrooms today, over 400 years later.

Answer: onion skin cells (macro)