Sunday, June 7, 2009

Addendum on the Texture

I woke up this morning thinking about the texture of the pickled walnuts, where you're eating all parts of the walnut fruit: the nutmeat inside, the immature nut, and the outer hull.

I was thinking that I should have said more in that last post about the texture, but I was having difficulty describing it. Then I figured it out and did a little checking this morning to make sure I was right.

The texture is rather grainy or gritty, and that's almost all due to a particular kind of cell in the hull. The texture is caused by "stone cells."

If you've eaten pears and quinces, this texture will be familiar to you, because it's the same thing. In botany classes, pears are the fruits the teacher commonly uses as "Exhibit A" for this cell type.

I hope I'm describing this perfectly accurately; my botany's sadly rusty. Stone cells are a type of sclerenchyma cell. (Here's how I learned to say it: "Sklair-IN-kah-mah.") Sclerenchyma cells are plant cells that develop a tough layer of lignin inside the cell wall; so tough and thick that the cell inside usually dies once the cell matures, because the layer is so heavy that nutrients and waste products can't get in or out.

Elongated sclerenchyma cells are the ones that end up in supportive roles, as in a tree trunk. You can also think about jute, hemp, flax, and other plant fibers that hold up well.

In the case of stone cells, instead of being elongated into woody fibers, the cells form as roundish little blobs, like cobbles, and apparently function in fruits in a protective role, holding off frugivory until the plant is good and ready for its seeds to be dispersed. (If you've tried to eat an unripe pear, you know what I mean.) Now imagine a caterpillar trying to swallow one of these little cobbles.

Stone cells come to their full glory as the walnut shell, the peach pit, the apple seed, the cherry stone, where the tender plant embryo is guarded from an herbivore's teeth and digestive tract even as the young new plant is dispersed away from its parent tree.

Anyway, "stone cells" explains the texture of the walnut hull; it has the same kind of grittiness as a pear or quince, and for good reason.

And I thought you might like a little botany lesson.

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