[in Japanese]

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The frequency of reversions, of the methionine-requiring mutant strain (4-24) of Ustilago maydis occurred spontaneously as well as by the X-ray irradiation and tris-nitrogen mustard treatment was studied and the nature of the reversions was discussed.
1. Spontaneous reversion takes place around at the rate of 3.0×10^-7 per cell per division, when cultured in the complete liquid medium.
The rate of reversional mutation was increased by both X-ray irradiation and nitrogen mustard treatment up to the orders of 10^-4. The mutation constant is calculated to be 2.2×10^-7 per roentgen.
2. Three types of reversions are discerned:
The pseudo reversion type (PR) appears as a result of residual growth and syntrophism. The complete reversion type (CR) and the inferior reversion type (IR) appear as a result of one gene mutation. The IR-type is distinguished from the CR-type by the restricted growth during early subcultures.

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[in Japanese]

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In this investigation the fertility and germination of the seeds of F₁ plants, and external characters, fertility and somatic chromosomes of F₂ plants of Triticum-Secale triple hybrids raised between F₁ of T. turgidum×S. cereale with T. vulgare were studied.
34 seeds were obtained from 4 plants of 2n=41 among 10 individuals of fertile Triticum- Secale triple hybrids, and 40 seeds from 6 individuals (66 spikes) of 2n=42 in the same hybrids.
No marked difference in fertility between these two groups of individuals of triple F₁ hybrids, having 2n=41 and 2n=42 chromosomes could be found.
The fertility in every individuals of triple F₁ having 2n=41 chromosomes has shown to vary 0.61-10.50 percents and that of 42 chromosomes to a 0.61-8.33 percents respectively. But these percentages of fertility are very low (Table 1).
The percentage of germination of F₂ seeds resulted from F₁ plants has shown to vary from 37.5 to 100 on the germinated seeds.
The somatic chromosome number of 40 individuuals of F₂ plants raised from 74 seeds resulted from the 10 individuals of fertile triple F₁ hybrids is very widely scattered from 28 to 56. The frequency of individuals for every number of somatic chromosomes has shown from 1 to 7; and these cases of dispersion of individuals for every class value (chromosome number) are almost all alike.
The somatic chromosome numbers of F₂ plants raised from F₁ of 2n=41 were dimodally distributed: 28-33 and 37-41, and those of the plants from F₁ of 2n=42 were 28-33 and 42-48.
In some individuals of F₂ plants the length of stems and density of spikelets were surpassing to those of parent, F₁ plants, in other individuals, however, not only no marked differences in the characters could be found, but some characters were rather inferior to those of the parent hydrid F₁ (Table 3).
The percentage of fertility of spikelets of F₂ in the case of self pollination has shown to vary from 1.91 to 132.87 percent, and the average value was 20.5 percent. In this case the fertility was improved 3-13 times, or 6 times in average than that of the parent F₁ plants.
The percentage of the fertility of fertile F₂ plants has shown to vary widely according to individuals. To summarize the fertility percentage for spikelets has shown highest in F₂ plants having 29-30 somatic chromosomes, and as the somatic chromosomes increase from these numbers, the fertility percentage drops gradually. And it shows the lowest in the case of the plants having 38-41 and 44 chromosomes, moreover, after that, in some individuals with 45-47 somatic chromosomes high percentage of fertility was shown again.

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In the previous paper the author reported that the male of reverted wild strain, which was obtained by the reverse mutation of short arista mutant and selected more than several generations, has peculiar Y chromosome of the following nature.
When a reverted wild male is crossed to short arista, or Delta, both on the III chromosome, sa or D behave as if they are sex-linked. When an Abrupt (sex-linked) female is crossed to a reverted wild male, the Ab character segregates as if it is an autosomal mutant. Furthermore when a female which has a lethal of semi-lethal factor on the one of her X chromosome is crossed with this reverted wild male, the effect of the lethal or semi-lethal factor on her X chromosome is suppressed. These unusual phenomena are explained on the basis of the presence of a peculiar Y chromosome in the reverted wild male. The author's hypothesis is as follows: 1. The Y chromosome in this species has a strong male determining factor, 2. A translocation between the Y and the III chromosome gave rise to a third chromosome with a part of Y containing the male determining gene; Thus, the reverted wild male has such a III-Y chromosome instead of a normal Y chromosome.
Furthermore, the author obtained recently two spontaneous recessive mutants, coarse and brown, which are both on the third chromosome. The result of genetic studies of these mutants indicates that the genes for these mutants are locate on the portion of the III chromosome which is homologous to that which is translocated to the Y chromosome described above. Crossing over takes place between the two. Crossing over also takes place between the III chromosome with D and the Y chromosome with translocation from the III chromosome, thus giving rise to a III-Y chromosome with D gene. The crossing over between X with Ab and normal Y chromosome occurs also. These crossing overs have occurred frequently in males.

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In experimenting various crosses of potato, one perfect male sterile potato plant was discovered. This plant readily functioned as female parent and no difficulty was found in obtaining seeds when pollen of normal plants was applied. The mature pollen produced by this male sterile plant is nearly normal in amount but its development is arrested. Germination tests were made with mature pollen of sterile and normal plants. In 20 percent sugar solution with 2 or 3 stigmas added, in sterile plant, no pollen grains germinated.
In 1946, a cross experiment was made between male sterile and normal male fertile plant (C 10). All F₁ plants were self-fertile, and all those tested had normal pollen.
In F₂ a ratio of 3 fertile: 1 sterile was obtained. Male sterility was completely recessive (Table 1). On the other hand, the results obtained from the other cross experiments in which C 20, C 21 and C 22 plants used for the reexamination the above experiment showed the digenic ratio in F₂ progenies, 15 fertile: 1 sterile (Table 2). These cross results indicate that male sterility probably depends on two recessive genes, ms₁ and ms₂ both of which are necessary for male sterility. And male-fertile plants contain either one or both of the dominant alleles MS₁ and MS₂. The genic scheme was represented as following:
ms₁ ms₂ …… male sterile
ms₁ MS₂ or MS₁ ms₂
MS₁ MS₂} …… male fertile

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Several morphological features of the nucleolus have been observed by the light microscope, although the majority of nucleoli appeared to be homogeneous masses. In the present experiment the periplasmodium nucleoli of Tradescantia reflexa have been observed with the aid of Shimazu magnetic electron microscope with an operating voltage of 50-140KV. In the central part of the metabolic nucleolus a lot of thread-substances are closely interwoven to one another. The peripheral part consists of a mass of fine threads giving the nucleolus a “honeycomb” appearance. There is no evidence of a limiting membrane surrounding the nucleoli.

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The seasonal spermatogenetic cycle was observed in the testis of the grass-frog, Rana temporaria, collected through the year in the vicinity of Sapporo, Hokkaido. Breeding occurs during from late March to the middle of April. During season, all spermatozoa are eliminated from the seminal tubules. The multiplication of the residual spermatogonia begins in early May and becomes active during June. Primary spermatocytes and the first maturation division appear from late June to July. The second maturation division and spermioteleosis continue through late June and August. Spermioteleosis is practically completed by the end of September or early October. No evidence of spermatogenesis during the winter period is observed.
There are a certain number of residual spermatogonia retained in a state of rest with polymorphic nuclei lying in close contact to the inner wall of every seminal tubule. They are clearly distinguishable from the tissue cells by their conspicuous apperance in both size and structure. They persist always as primordial spermatogonia. After the discharge of spermatozoa in the breeding season, the residual spermatogonia repeat active divisions and start the new spermatogenetic cycle in preparation for the coming season.

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In the present paper chromosome numbers of some dicotyledonous water plants are reported. The results obtained by the writer in 14 species (9 genera, 4 families) are given in the table including the previous results of other authors.

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1) In dieser Arbeit wird der morphologische Unterschied zwischen den in der Natur wachsenden, intraspezifischen Polyploiden von Dumortiera hirsuta, nämlich Monoplont (n=9), Diplont (n=18) und Triplont (n=27), miteinander vergleicht.
2) Entsprechend der Verdoppelung der Chromosomenzahlen ist die quantitative Vermehrung der Grösse einiger morphologischer Merkmalen der Polyploiden beobachtet, aber kein qualitativer Unterschied der Merkmalen wird wahrgenommen.
3) Die Chromatophorengrösse in den Diplonten sowie auch in den Triplonten differiert wohl kaum mit derjenigen in den Monoplonten.
4) In den Diplonten dieser Art sind die Kern- sowie Zellvolumen wenig kleiner als doppelt so gross wie diejenigen der Monoplonten. Der Grad der Vergrösserung von Diplonten lässt sich bei den Geweben sowie Organen noch mehr vermindern. Daher sind die Grösse einiger Organen der Diplonten wieder auf diejenige der Monoplonten beinahe zurückzukommen.
5) In den Triplonten dieser Art sind die Kern- sowie Zellvolumen etwas mehr als dreimal so gross, als diejenigen der Monoplonten. Dieser Vergrösserungsgrad wird bei vielen Geweben und Organen der Triplonten noch mehr vermehrt. Aus diesen Tatsachen kann man daran folgern, dass es nicht immer die Annahme (Wettstein 1925, '40, Darlington 1932) bestätigt ist, dass die Artkonstante der intraspezifischen Polyploiden mit der Vermindung von Grösse der Merkmalen zusammenzugeht sei.
6) Die Artkonstante dieser intraspezifischen Polyploiden möge wohl wegen seiner Allopolyploidie, und der Vergrösserungsgrad seiner morphologischen Merkmalen auf das Zahlenverhältnis van Allo- und Autogenomen jedes Individums zurückzuführen sein.

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