Summertime is watermelon time

I am sympathetic to Roger Doiron's crusade to eat locally on July 4, but have to admit that my desire for watermelon on Independence Day ruled that out for me.

I'm in Boston, where no watermelon will ripen in fields for quite some time yet. But I grew up where watermelon was a local crop harvested by the Fourth, and I simply can't imagine a summer picnic without it. For Independence Day, it's an inviolate tradition at my house.

But as rivulets of red juice ran down our chins at the end of our cookout Saturday, we discussed the appeal of the big red and green fruit. And several people had watermelon questions they'd always wondered out.  These were directed at me, as the so-called expert on all things horticultural. (Or at least the person closest at hand who was most likely to know the answers.)

Question 1: Where did watermelon originate? Is it an American fruit? No, I said, it originally came from Africa (National Geographic confirms that) and Egypt (which is, of course, northern Africa), but has been grown around the world for thousands of years.

Question 2: Why do seedless watermelons almost always have a few seeds? And why are they then called seedless if they aren't? Part of the answer to that comes from understanding how seedless melons are developed. (How can you get seeds if the fruit is seedless?)

Here's a relatively simple explanation from the Texas Agricultural Extension Service:

The number of chromosomes (the threadlike bodies within cells that contain the inheritance units called genes) in a normal watermelon plant is doubled by the use of the chemical colchicine. Doubling a normal (diploid) watermelon results in a tetraploid plant (one having four sets of chromosomes). When the tetraploid plant is bred back, or pollinated, by a diploid or normal plant, the resulting seed produces a triploid plant that is basically a "mule" of the plant kingdom, and it produces seedless watermelons.

What you call "seeds," Jerry Parsons of the Texas Agricultural Extension Service refers to as "white seedlike structures that are edible."

Donald Maynard of the Florida Extension Service  provides more detail:

Small, white rudimentary seeds or seedcoats, which are eaten along with the fruit as in cucumber[s], develop within the fruit. The number and size of these rudimentary seeds vary with variety. An occasional dark, hard, viable seed is found in triploid melons.

Question 3: Why isn't this melon cold? Well, the obvious answer is, there's only so much room in one refrigerator. But last summer, a neighbor told me something about watermelon I'd not known before. It's best to store an uncut watermelon at room temperature, because it will be more nutritious than a cold melon. (Of course, after cutting, the watermelon has to be refrigerated.) But that's interesting because it's the opposite of what you might think.

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