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True homnozygotes of Nicotiana tabacum L., herein referred to as Ky Iso lines, are being developed from haploids. A technique is described whereby seedlings resulting from fertilization are eliminated, leaving only suspect haploids. After confirmation, haploids are treated to double the chromosomes and these result in completely homozygous plants. One complete homnozygote, Ky Iso 1 Ky 16, has been developed and shows extreme uniformity in all characters studied. The Ky Iso lines will be useful in genetic stuidies that require no plant-to-plant genotypic variability. The Ky Iso lines will be made available upon request as they are developed.

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OBACCO, Nicotiana tabacum L. ( n = 24), originated as an amphiploid of T N . sylvestris ( n 12) (section AZatae) and N . tomentosiformis or N . otophora (n = 12) (section Tomentosae) of the genus Nicotiana ( GOODSPEED 1954( GOODSPEED , 1961. The raw amphidiploid had many gene duplications in its genetic complement, since it actually had twice the amount of germ plasm necessary to sustain a species. This amphidiploid evolved through gene mutation and natural selection into the present day tobacco. Probably one or the other member of a duplicated vital gene pair could mutate and thus establish a simplex condition for that gene without deleterious effects usually associated with mutation. In tobacco there are some traits, such as chlorophyll production, that are conditioned by duplicate factors. It is likely that the two subgenomes that constitute N . tabacum still maintain some of their genetic individuality as duplicate factors and to that extent each could carry out some particular vital process independent of the other. This partial independence or interdependence of the sets of chromosomes within the N . tabacum genome is a good index of the progress towards diploidy in this species. The present study was designed to study this phenomenon of subgenome interdependence in N . tabacum by finding the range of heteroploidy in the F1 progeny of a haploid x diploid tobacco.Haploidy in N . tabacum was first reported by CLAUSEN and MANN (1924).KOSTOFF ( 1943) divided the haploids into two groups, parthenogenetic and androgenetic, depending upon the nature of the gametic cells (eggs or sperm) from which they developed. Both parthenogenetic and androgenetic haploids have been observed in tobacco ( CLAUSEN and MANN 1924; CHIPMAN and GOOD-