Seedless watermelons are particularly interesting because they must be propagated by seed, and yet growers can still exploit parthenocarpy. One way to make seedless watermelons is to produce triploid seed. As in the case of bananas, triploid watermelons cannot produce functional seed, but they still develop good fruit through parthenocarpy. Plant breeders produce triploid seed by crossing a normal diploid parent with a tetraploid parent, which itself is made by genetically manipulating diploids to double their chromosome number. In the case of watermelons, this manipulation has to be performed each generation, so it is a somewhat expensive proposition but still worthwhile.