1. The comparison of chromosomes was made between 7- and 8-chromosome rye regarding their, size, shape and behaviour in PMC-s and pollen grains.
2. In common rye, the chromosome number was counted to be 7 at metaphase of primary nuclear division in pollen grains. These chromosomes were classified into three groups according to their size and shape.
3. During the meiosis in 8-chromosome rye, 8 bivalents showed rather regular behaviour, and 8 chromosomes were counted in the majority of their pollen grains.
4. Chromosome set of 8-chromosome rye consists of 7 chromosomes quite similar to those of 7-chromosome rye and an extra small chromosome.
5. The extra chromosome is not the same in its size and shape as the k-chromosome in GOTOH's 8-chromosome rye.
6. The position and shape of nucleus in pollen grains is usually characterized by the stages of their development, and we can distinguish by these the vegetative and the generative nuclei.
7. The extra chromosome shows rather irregular behaviour in primary nuclear division of pollen grain. In most cases, two halves of it were included in the generative nucleus or remained lagging, so that the vegetative nucleus receives 7 ordinary chromosomes.
8. From the irregular distribution of the extra chromosome, the plants having 14, 15 and 16 chromosomes in diploid may be expected in the offspring of 8-chromosome rye.
The writer wishes to express his gratitude to Prof. Dr. KAGAWA for his valuable advice, and is also indebted to Prof. Dr. TABATA for the permission to use the material under his management.