Wikipedia Article About Watermelon seeds on Wikipedia Although so-called "seedless" watermelons have far fewer seeds than the seeded varieties, they generally contain at least a few soft, pale seeds. They are the product of crossing a female tetraploid plant (itself the product of genetic manipulation, using colchicine) with diploid pollen. The resulting triploid plant is sterile, but will produce the seedless fruit if pollenized by a diploid plant. For this reason, commercially available seedless watermelon seeds actually contain two varieties of seeds; that of the triploid seedless plant itself (recognizable because the seed is larger), and the diploid plant which is needed to pollenize the triploid. Unless both plant types are grown in the same vicinity, no seedless fruit will result.