(b) Chromosome number instability
One of the cobinspicuous phenomena would be chromosome number instabilities that appear in certain hybrid combinations. Variations in somatic chromosome number were observed, as described above, in the backcrossed progenies of the hybrids between A. ciliare as female crossed with hexaploid wheat or H. bulbosum, and either A. tsukushiense or A. repens as female with H. bulbosum (Shigenobu-Kishimoto and Sakamoto 1982; Kaneta and Muramatsu 1983a, b).

Much more extensive chromosome number variation than described previously among cells within a plant was found in the cross combination using barley cultivars, H. vulgare. To rule out any artifact in producing the microscopic preparations, the hybrids were reinvestigated in 1988 and the same tendency of the wide chromosome number variation was confirmed (Muramatsu et al. 1989).

Detailed observations made on the hybrid materials in 1988 showed that the chromosome numbers varied very widely from 14 to 41 when A. ciliare was used as an Agropyron parent crossed to barley. In the leaf blade of the hybrids there were several clear sectors, which showed different degrees of tinctures, strongly suggesting chromosome instability (Muramatsu et al. 1990). In addition, there was clear difference in plant growth, which may not be caused by chromosomal anomalies but may rather constitute genetic hybrid weakness. The hybrid plants involving H. vulgare as parent showed strong growth inhibition so that plants remained very small and barely had any spike. On the other hand, nearly normal plant growth was seen in the combination with H. irregulare.

Further investigation was carried out in the hybrid involving A. tsukushiense. As shown in Table 6, of 32 hybrid plants obtained and investigated, all of the plants showed somatic chromosome instability. Cellbis with somatic chromosome numbers from 14 to 56 were observed in A. tsukushiense x H. vulgare, and from 22 to 53 in the hybrids involving H. irregulars as barley parent. In both combinations the expected numbers of 2n=4x=28 were observed in 63.9% of cells in the former hybrid and in the latter 62.2%. Spike morphology showed big differences among tillers: spikelet per node showed the character of Agropyron to barley type that is 3 per node. It is important to note that an individual with 2n=21 cells frequently had spike morphology resembling the Agropyron parent Made et al. 1990; Uno et al. 1990).

When the fluctuation leads toward the reduction of chromosome numbers, and if the entire barley chromosomes were eliminated. polyhaploid of the Agropyron could be produced. Such tillers or individual plants were formed during the development of the hybrid plants. The elimination process was relatively gradual in the combination of Agropyron line "Nakayamashouten". In Fig. 8, a spike of such a polyhaploid plant (2n=3x=21) of A. tsukushiense is shown. The same phenomenon of the barley chromosomes was observed in the different A. tsukushiense line, and also when A. humidorum Was used as female parent. The elimination seemed to be the same with that in the A. tsukushiense hybrids, and resulted polyhaploid plants of A. humidorurm (Muramatsu et al, 1992, 1993; Nakatsuji et al. 1992), Hybrid plants with the reduction of barley chromosome are shown in Fig. 9, and somatic chromosomes in root tips of a polyhaploid-A. humidorum (2n=3x=21) are shown in Fig. 10.

(c) Successful production of amphiploid in relation to the genetic differences
Throughout the investigations, artificial induction of higher auto- and allo- polyploid were tried many times. Whenever it was possible the hybrid plants were treated with a colchicine solution to produce chromosome doubling. With the same treatment given and repeated for years results were clearly different among the cross combinations. In one of the studies to compare the effect of the colchicine between different cross combinations, seven different cross combinations - where the hybrid plants obtained involved embryo rescue or not- were compared (Muramatsu 1985*, Uno and Muramatsu 1989). As shown in Table 7, fertile sector never appeared in the F₁ plants of A. tsukushiense x 6x-wheat and A. tsukushiense x rye, despite the treated tillers clearly showed strong effect of the colchicine solution. On the other hand, the rest of the hybrids effectively formed fertile sectors. The method used was either that of Sears (1941), or of Winkle and Kimber (1976). According to the present author's experience - if properly treated - there is no large difference between the methods of treatment at least in obtaining an amphiploid line, e. g. in the Table 7 F₁, T. spelta x A. intermedium, was by the latter method (Muramatsu and Sigunga 1983).

Clearly, the successful inductions were limited in certain combinations. With repeated experiments, I have never obtained induced octaploid (8x) strain in A. ciliare, (2n=4x=28, allotetraploid), while octaploid lines (2n=8x=56=AAAABBBB) have been produced in the tetraploid wheats. The author would like to state here a thought of genotypic control for polyploidization; that this difference was throughout the later experiments consistently confirmed. Therefore, I should like to suggest the idea that there is apparently a biological condition for the persistence of certain ploidy. Presumably, genotypic control is involved, that is to say that certain level of amphiploidy is only maintained with a kind of genotype for that ploidy. If we think of that condition, we may have to find a term to designate it, and the author proposes that such kinds of genotypic properties be called "definitomodis genetic conditions"**. Only under that determination of range or level of zone multiplication of chromosome sets will be possible, and a fit ploidy will be realized.