1.水稲において³²Pをmutagenとして使用した場合の有効な選抜法を究明するため，R₁の節とその後代にあらわれた変異型との関係について調査を行つた。2.主稈および各1次はそれぞれ独立Lた変異を生ずる場合が多いが，時には同一変異型が共通に認められる場合がある。この場合，変異型の出現する1次は主稈を対象に区分キメラ的にあらわれることが多い。3.下位分藥ほど変異型の出現頻度が高い傾向があった。4.変異型の出現については，2次および3次はこれらが従属する1次および2次との間にそれぞれかなりの相同性がみられた。5.R₁稔性とR₂穂別系統における不稔系統出現との間にはかなりの相関が認められたが，一方R₁穂稔性とR₂穂別系統内における稔性変異を除いた変異型の出現頻度との間には特に関連は認められなかった。6.以上の結果より，R₁およびR₂の取扱いについて若干の考察を試みた。

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1. With the aim of inducing reciprocal translocations of chromosomes in rice, soaked seeds of four varieties were x-rayed with the dose of about 20, 000 r. The plants from the treated seeds (X₁) and their progenies (X₂) were investigated. 2. The fertility of X₁ plants was remarkably reduced. 80% of main heads showed less than 50% fertility and those with the fcrtility under 20% were the commonest. No difference was found among the varieties in the degree and the mode of sterility. The reduction was aiso found in the number of tillers. 3. The sterility of tillers from iower nodes somewhat differed from that of main culm in X₁ generatiori. The secondary tillers had generally the same degree of sterility with primary ones from which they grow.

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In 1949 young F1 seedlings of 9 penta.ploid crosses between A1;elace barbceta (n=14) and some culti-vated varieties of Ave, na sativa (n=21) as well as A. nuda(u=21) vrere treated with 0.05% colchi cine solution according to L., b. CUA's method(951). It was already reported that pentploid Aveu hybrids were highly sterlie (I:ISHlYAltlA 1929, 19 39). Howeveir, same of the: treated hybrids were found to exhibit different degrees of fertility. It was further noted that different ears in one and the same plant often showed a great var'iation in fertility ranging from 'highly fertile to completly sterile (Table 2) . In the present case it is beyond doubt that 'che fertile plants would be amphidirp lojds of pentaploid hybrids. A preliminary investigation rewaled that some seedlings from fertile plants hd 70 omatic chromosomes as expected. Basing on the degree of fertility the auth=0f elas-sified the treated plants as 4la plants (high fer-t, ile), 2 u:1a mixoploids (either low in fertility or having soine ears that, are highly fer'ti', , e but the others age sterile) and 2n plants (nearly colenpietely sterile-). The resits are given in Tables I and . In this work 6 different amphidiploids (dctoploid oat) were succesefully obtines and the offspring ar, e novT'grow. ing vigorqusly in the field.

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異なる水位上昇速度下で栽培した浮稲の主稈と分げつの乾物生産並びに葉面積の変化を調べた.深水により弱小な2次分げつの乾物生長速度が低下するのに対し, 主稈や1次分げつのそれはむしろ大きく, 稈への乾物分配も大きくなった.すなわち, 浮稲は個体の生長に最も有利になるようにシンク・ソースのバランスを変化させて深水条件に対応しているものと考えられた.

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In the present paper, the authors discuss about the serial order of following six genes belong to the :P1-linkage group. P1 : The modifyer which distributes janthocyanin pigment over the whole leaf blade, Ieaf sheath, as well as pulvinus and stem node. Rp : The modifyer reponsible distributing apiculus, color over the whole surface of palea, Iemrila and rachilla. Ph : The gene for phenol reaction. The carybpsis, and glume of certain rice varieties are stained with dark violet color by phenol treatment. This characteir behaves as dominant over negative phenol reaction or non-coloring. lg : The gene for liguleless. d₂: The gene for "Ebisu" dwarf. d₃: One of the multiple genes refers to "Tilleringdwarft " . Of these genes, the following recombination values were calculated in F₂ segrega, tion.

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自殖性作物における，あたらしい突然変異育種法として累代照射による突然変異誘発をとりあげた。これは毎代照射をくりかえすので，いつも翌代に新しいX₂系統の栽培が可能であり選抜の対象とすることができる。毎代種子に放射線照射をくりかえすことによって，照射集団内の遺伝的構成がどのように変化するかを数学的'にとりあつかった。翌代に突然変異体を分離する系統の割合は6代照射以後ほぼ一定値をとる。また，突然変異体がほかの遺伝子型(原型やヘテロ個体)とおなじ・繁殖率をもつと仮定すると，突然変異系統の割合は世代をかさねるとともに増加してゆく。そのために照射集団は突然変異集団に転化して選抜が容易とたることが予想された。イネ種子にγ線照射を毎代等線量でおこない，1.回照射と累代照射とのあいだで不稔や突然変異について比較、Lた。照射回数をまLても不稔に関して放射線感受性の変化がみとめられないこと，および累代照射をおこたう'ことによって不稔のちく積がおこることはないことが観察された。毎代，10，OOOrをあたえていったときには照射回数とともに突然変異もましていったが，30，000rの照射をつづけたときには突然変異がまさなかった。そのため，累代照射においては高線量照射はのぞましくないと結論された。また，累代照射によって突然変異スペクトルの幅がひろくたり，まれな突然変異型がみいだされ.るようにたった。さらに，イネとオオムギとをもちいてX線照射を3代くりかえし，照射集団ではベテ阿個体が保持されていることをたしかめた・また，照射集団において3回目の照射によって生じた突然変異頻度は1回照射のときの突然.変異頻度とほぽひとしかった。このようにして，累代照射によってたかい突然変異類.度がえられるのは，集団内における突然変異体の増加を別とすれば，主として照射集団内にヘテロ個体が保有されていることにもとずいていると考えられた。

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1. To make clear ecologicai characteristics of auto-tetraploid in rice plant, diploid plants of six varieties and the auto-tetraploid ones induced artificially from each of them were used. They were exposed to various environmental conditions, i. e. natural conditions, short day, Ioilg day, high Lem-perature, early sowing, and iate sowing. Gtowth, date of heading, and fertility were investigated to corxipare the tetraploids with the diploids. 2. There was a tendency that tetraploids were. superior to diploids in the elongation of their heiaht from tillering stage to the booting stage. But as fbr the height of plant after he.ding.", the tetraploid were c, .earfy lower than diploids. The cause of this seems to lie in the fact that the d.iploids are very superior to the tetraploids in the length of the first interriode Sust Jender the ear. 3. In bomparison with diploids, the date of heading of the tetraploids was little later or nearly equal in the Japanese late varieties. This tehdency was more clear in Java N0.28. On the contrary Aikoku (middle variety) and P.hiiippine No. 5, were hastened. 4. Between the diploid and tetraploid of Philippine No. 5, there was a difference in photoperiodic resonse. The heading of the tetraploids was earlier than the diploids in aH the other treatments except short day treatment in which the former was later than the latter. Ear formatiori of diploids did not occur under the long day condition but in the tetra-plaids, it was perfectly indifferent to this condition. 5. These-facts will furnish same new valuable data on the problems of adaptation and geographical distribution of polyploid plants.

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1. Using eight varieties of wheat, which are classified into three major groups of different earing habit (See Tabe 1), a number of transplantings of immature embryos into deyeloping seeds was carried out. An excised immature embryo of a foreign or its owh variety was inserted into the endosperm of a developing seed as depicted in Fig. 1., thus obtaining the matured viable seeds, each with two embryos, one of which is the proper and the other the transplanted. The author succeeded in raising a large number of such artificial twin seeds, eacb of which consists of two embryos of different varieta.1 nature or of the same. The pairs of plants were grown up from a number of such twin seeds, and their flowering responses were examirLed, making comparisons within each pair of sister plants as well as among the dlfferent pairs derived from various varietal combinations (See Table 3). 2. There can not be noticed any differences among the earing responses of the plants grown up from the transplanted embryos which, have the same genetic constitution but matured under different endospermous condition of the foreign varieties. In other words, those plants develop a quite similar number of leaves on their main stem before the ear-emergence, resuiting in neither promoting nor delaying the anthesis. The plants grown up from proper intact embryos of those twins show also quite similar situation in their earing behaviour, i. e., an additional transplanting of a foreign embryo having different earing habit into the developing seed does not exert any discernible influence on the earing character of the proper intact ernbryo.

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Since 1943, it has been intended to breed the resistant varieties to rice-blast by hybridization between one of the foreign varieties in Japanese-type which offered resistance to a high degree and some of the Japanese varieties in rice.As the result, it was succeeded to obtained these varieties, "Kanto-No.51", "Kanto-No.52", "Kanto-No.53", "Kanto-No.54"and"Kanto-No.55", all of which have higher resistance to rice-blast compared with any variety of rice in Japan.

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Prophyllが枯死して識別できない場合でも主稈の止葉葉位がわかれば各蘖子の着生節位とその葉数(止葉)を確認できる方法を利用して、株内全蘖子の出穂日を記録しておき蘖子の次位・節位と出穂日との関係を調べた。

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