The somatic chromosome numbers of two species and one variety of Hosta were ascertained: H. clausa and its var. normalis are 2n=90, and H. ventricosa 2n=120. Accordingly H. ventricosa is tetraploid, and the other two are triploid. The 90 chromosomes of H. clausa var. normalis were in 45 pairs, which could be classified into six pairs of large chromosomes, three pairs of medium ones, and 36 pairs of small ones. The karyotype of H. clausa differed from that of H. clausa var. normalis in the numbers of large chromosomes and medium ones. There were a number of pairs uneven in form. H. clausa is considered to be an allotriploid species which had presumably been derived from H. clausa var. normalis. H. ventricosa is considered to be an allotetraploid species of an autotetraploid origin. These three entities are, from their geographical distribution and karyotypes, considered to have descended from a common prototype.
Electron microscopic studies were made on the cell division and fine structure of Agrobacterium tumefaciens. Two types of cell division were observed, the one being a division starting from the constriction at a middle part of the bacterial cell, and the other beginning with a septum formation inside the cell. The former type of division was found to be commoner than the latter. Concerning the fine structure of non-dividing cells, the cell was enveloped with a double membrane sandwiching a layer of low electron density. Inside this membrane, a dense protoplasmic membrane and a double-layered intracytoplasmic membrane were observed one after another. Within the cytoplasm, two kinds of granules were observed: the one ca. 5mμ in diameter (perhaps protein or lipid granules) and the other ca. 15mμ in diameter (perhaps protein bodies). Besides, highly electron-dense particles of about 50mμ in diameter were sometimes observed in the cytoplasm. A so-called 'nuclear region' of lower electron density was also observed along the long axis of the bacterial cell. This was composed of numerous filaments seemingly corresponding to DNA. Around the nuclear region, double-layered membranous structures were frequently discriminated. Fine structure studies on the nuclear region of this bacterium may serve to provide an important clue for the elucidation of the intrinsic nature of bacterial nucleus in general.