Cytogenetic Studies in the Artificially Raised Interspecific Hybrids of Papaver

1. The chromosome number in the F1 plant between Papaver No. 41, 8 (a bracteata like tetraploid Papaver) and P bracteata is 21 which is the sum of the gametic chromosome numbers of the parents. The chromosome association in the meiotic phases of the PMCs is generally 2III+6II+3I, but rarely 2III+4II+1IV+3I. The 2II in 6II of the former formula is derived from 1IV of the latter.2. Papaver No. 41, 8 has 28 chromosomes which synapse to form 14 gemini in the PMCs, while the haploid complement has the constitution 2II+1III+7I (YASUZ, 1937). This fact together with the above mentioned data led to the following conclusions as to the relationship between the basic chromosome complements in Papaver No. 41, 8: 1), the haploid chromosome complement of No. 41, 8 consists of the 2 basic complements, (B) and A; 2), (B)-complement is homologous to the haploid complement of P. bracteata (B-complement); 3), three (A1-3 ) of 7 chromosomes in A-complement have homologous chromosomes-(B)1-3 and B1-3 in Table 5-either in (B)- or B-complement; 4), the fourth chromosome (A4 in Table 5) has homologous ends which is homologous to one end of the third chromosome in all these three kinds of complements; 5), the remaining three of the A-complement have no homologous chromosomes in (B)- or B-complement (cf. Table 5).3. Papaver No. 41, 8 is a tetraploid in terms of chromosome numbers, but it is an incomplete tetraploid in the sense of the chromosome constitution, because on one hand in one (A-complement) of 2 basic chromosome complements one component chromosome is lacking, so that it is incomplete, and on the other hand one chromosome is added which is duplicated by one part of another component chromosome.4. The structure of the synapsed chromosomes in the F1 plant and the relationship between the chromosomes and the nucleoli were discussed.5. The irregular behaviours of the chromosomes in the meiosis of the PMCs of the F1 plant result in high abortion of the pollen grains, but the sporadic seed formation by the back cross with the pollen grains of the male parent shows that some egg cells are fertile.Here the writer wishes to express her best thanks to Prof. Fujii for his valuable advice throughout the course of the work. The expence of carrying out this study were partly defrayed out of a grant from the Science Research Fund of the Department of Education.