"My understanding is if you grow a large field of seedless watermelons you will end up with three types of melons. The normal fruit of the diploid pollinator, the seedless fruit, and a small number of fruit that is different than the other two. This melon contains the seeds for next years seedless planting." Unfortunately, not true. You have to use the breeding lines to create new seeds each year. That is the same with regular hybrids, except that extra steps must be taken to set up the breeding lines.

If you want to this for the fun of experimenting, than just try something that you'd like to eat and see how it works. :) Watermelon seeds used to be good play with, but the grocers only sell the seedless ones now. Although my BIL came up with a seeded melon last weed! Last year I got some canteloupe seeds to sprout, but the ra(t)bbits ate them. Seeds need to be left on the plant long enough to ripen, the "seeds" you find in cucumbers arent mature enough to grow. You can occassionally find heirloom tomatoes at the organic stores, all you can do is try! You can get basic veggie seeds during the spring for less than a buck, sometimes even 10 cents!

I have planted things from store bought food- peppers, oranges, grapefruit, lemons, watermelon, etc. The peppers actually have turned out great- wonderfully sweet, and for now, everything else has grown (just waiting for them to mature to see how it turns out). From what I hear, you never know what you will get from the seed- but it will most likely grow. All mine have. Give it a try. Might turn out well for you!

But it actually raises an interesting thought: For the heirloom tomatoes to come true from seed, they (like the Sungold's inbred parent lines) must be entirely homozygous at every loci. Otherwise you would get variation in the progeny. **** True that OP's should be homozygous for all genes but despite that one can see biological diversity, genetically, within a specific variety b'c nothing is static in terms of seed germplasm. Those with eyes that can see can put out 10 plants of a specific variety and see subtle differences in leaf form, internode distances, etc. (Which means that the heirlooms are stable because they're so inbred they've lost all extraneous genetic variability. Who would have thought that the Sungold F1 has more inherent genetic diversity than Brandywine?) As I mentioned above OP's are not devoid of the capacity for genetic variability. Since most of the many parental inputs into hybrids, Sungold F1 included, are single genes for some systemic disease tolerances, high solids content, the uniform ripening gene so there are no green shoulders, etc., that doesn't necessarily say that there's more genetic variability with Sungold F1 or ANY hybrid as I see it than there is in an heirloom variety. it's been estimated that about 95% of the heirloom varieties arose by natural cross pollination and then someone making selections from that initial hybrid and stabilizing it out to a stable OP, so there's lots of genes in there from two other complete genomes that have sorted themselves out by gene segregation as the selection process goes forward. The other 5% of heirlooms are said to come from mutation from existing varieties whether that be by Seed DNA mutations or more rarely by somatic DNA mutations within the DNA of a plant cell. Carolyn