Tomatoes Heirloom vs Hybrid
It is my understanding that one cannot plant tomatoe seeds from a Hybrid plant and expect to get the same plant. My question has to do with Heirloom tomatoes that were developed by crossing different varities. Specifically the Mortgage Lifter that is the result of cross breeding four different varities. Why will the Mortgage Lifter, a Heirloom, produce the same fruit from seed, when an Early Girl, a Hybrid, will not?