Tobacco seedlings from progeny of a single aberrant plant, either self-fertilized or used as the female in crosses, failed to become autotrophic at 13 degrees day and 8 degrees night temperatures, but grew normally at 26 degrees day and 20 degrees night temperatures. After initial normal growth at 26 degrees day and 20 degrees night temperatures, autotrophic plants from the aberrant line also died after subsequent exposure to 13 degrees day and 8 degrees night temperatures. The temperature-sensitive lethality was transmitted only through the female parent. When seedlings were grown at normal 26 degrees day and 20 degrees night temperatures, mutant selfs, normal selfs, and reciprocal F(1) hybrids were indistinguishable.