Botany Within Your Reach – 2. Onion rings

When TPP asked a group of youths if they had any botany questions, one bright young thing asked how they make onion rings?  Now clearly here’s a youth who never helps in the kitchen, which is probably not their fault, or from one of those unfortunate families that don’t actually need a kitchen since they never use it to cook. Now here’s an interesting image of something not so common, and yet not rare or unusual either, and it provides you a hint for answering the onion ring question.  So before moving on.  Anyone?  Anyone?

It also helps if you can answer the question about what part of the plant you are eating when you eat onions? (Hint: The range of answers is root, stem, leaf.)  Clue: it isn't a root or a stem.  To proceed further, cut any available onion down the middle, top to bottom, and look at what you have - a short, broad stem (the button at the bottom) bearing modified leaves.  If the outer layer(s) are yellow brown, the “skin”, you have some dehydrated leaves whose cuticles on the top and bottom epidermis provides some water-proofing, a natural wax paper, to protect the fleshier leaves within.  There may even be a few bits of dried roots attached to the bottom of the stem, but generally you cut the stem off and discard it.  So the oldest leaves are on the outside and they get progressively younger as you move up (inward) the stem. 

Get another onion. Now cut this one in cross section in the middle and you see concentric circles of modified leaves, a lot like the image above. Make a second cut parallel to your first slice and, voila, onion rings. Here’s the interesting thing, in most monocots and a few basal dicots leaves encircle the stem. This poses as engineering problem as each successively younger leaf is within the next oldest leaf, so how do it get out? Sometimes part of the leaf is discarded (e.g., Magnolias, Pipers), or the younger leaf grows out through a hole of slit in the older leaf.

So you don’t make onion rings in a manufacturing sense, but you must cut your onion the correct way. The image above is from a leek, a relative of onions; another species in the same genus, an ingredient in cock-a-leekie soup, a nice recipe from the homeland. In the case of leeks, the leaves are white at the bottom and turn green as you go upward.  These cross sections were cut near the point where a slit of the side of each leaf forms to let the next oldest leaf grow out.The larger vascular bundles in the leaves show up as darker green spots. So now you know what onion rings are. 

It's also OK to let your kids use knives in the kitchen. TPP finds that after losing one or two fingers they tend to be better students who are more attentive even if they cannot count as high.