The onion epidermal cell provides a protective layer against unwanted viruses that may harm the sensitive tissues. Because of its simple structure and transparency it is often used to introduce students to plant anatomy. These properties also make it useful for demonstrations of plasmolysis. The clear epidermal cells consist of a single layer and do not contain chloroplasts, because the onion fruiting body (bulb) is used for storing energy, not photosynthesis. To prepare onion epidermal cells for microscopy, smaller onions that feel firm are best. Remove the epidermal layers by cutting the onion and peeling them off (they are the membrane-like sheaths between each onion layer). For advanced microscopy, such as fluorescence microscopy, the layers halfway between the outside and the centre of the onion are best.
If you are using these layers for biolistics, it is important to note that bombarding with the cells facing up or down, on the media that they're placed, on can't make a difference.
Famous quotes containing the words onion and/or cell:
“But could a dream send up through onion fumes
Its white and violet, fight with fried potatoes
And yesterday’s garbage ripening in the hall,
Flutter, or sing an aria down these rooms
Even if we were willing to let it in,”
—Gwendolyn Brooks (b. 1917)
“In America all too few blows are struck into flesh. We kill the spirit here, we are experts at that. We use psychic bullets and kill each other cell by cell.”
—Norman Mailer (b. 1923)